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4-20mA process signal: (See Sensor in Glossary)

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A

Alarms & Control Points: (See Set Points in Glossary)

            High Level: (See Set Points in Glossary)
            Low Level l: (See Set Points in Glossary)
            Make Up: (See Set Points in Glossary)
            Sump: (See Set Points in Glossary)

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B

Bubbler Concept:

The Bubbler Concept is simple to understand by telling a "simple bubbler story" we all relate to:
           ·your eardrums are the level sensor in the bubbler system
           ·the air in your lungs is the bubbler air supply such as plant air.
           ·a straw stuck in the bottom of a glass of water is the bubbler stand pipe.
     If you have to blow the water out of a straw that's stuck in a glass of water it's no problem. Your eardrums, the level sensor, don't experience anything out of the ordinary and you are able to easily keep the water from pushing its way back up the straw. That's done by maintaining enough air pressure in the straw to overcome the weight of the water covering the straw or the bubbler tube.
     Now, let's move over to the local swimming pool and stick a 10 foot long straw in the water. Again you're going to blow all the water out of the straw or bubbler tube. Remember your lungs are "plant air" and your eardrums are the "level sensor". At some point your eardrums will begin to sense the change in back pressure created by the weight of the water trying to push up into the straw. Eventually, when you push out all the water your eardrums, the level sensor, will experience the total weight or back pressure created by the height of the water covering the straw at that depth.
     In a bubbler system the EXACT same situation is at work. Plant air, flowing at a very low flow rate and a pressure slightly more than the maximum back pressure or weight of the water covering the bubbler tube keeps the liquid out. A 'tee' connection is inserted into the bubbler line somewhere between the air source and the end of the bubbler tube has a 4-20mA sensor attached to it. The sensor is usually located in the same enclosure as the DistaView® controller. The sensor is now "touching" or sensing the changes in pressure caused by the water level going up & down. As the pressure changes the sensor converts it into a usable 4-20mA process signal. The 4-20mA signal is sent to the DistaView ® controller, or any other device that can use this type of analog signal. An analog signal is the same as saying continuous level measurement or monitoring.
     Now you can see why any size air leak in the system is a very big problem. The bubbler stand pipe has to be made of a material that will withstand the caustic material or high temperature effects from the liquid it's submerged in. It can be 1/2" to 3/4" ID. This is why a bubbler can be used in slurry, chemical, molten, and explosive environments. It is also an excellent choice for miniature level applications such as filling car batteries or laboratory procedures in test tubes and vials. The bubbler tube can be as small or large as necessary.

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Bubbler Stand Pipe:

This is an actual piece of pipe or tubing that is submerged in the liquid you want to measure or control. The bottom of the tube must be located lower than the Low Alarm level you need for the application. The bubbler stand pipe has to be made of a material that will withstand the caustic material or temperature effects from the liquid it's submerged in. It can be 1/2" to 3/4" ID. It is absolutely critical that there are no air leaks between the air supply entering the threaded fitting on the bubbler enclosure to the end of the bubbler tube. An air leak anywhere in the system will cause the controller to display the wrong Actual Level and provides less than consistent operation.
(See Testing a NFA Bubbler PDF for more information.)

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Bubbler System:

The "bubbler" is a level sensing technique or device that is used in the same way you would use an ultrasonic, laser, direct contact pressure sensor, probes and load cells. Each application has a "best sensor choice" and in many applications the "bubbler" is it. Many times it is the ONLY choice. This type of system is ideal for materials that are difficult to manage because of foaming action, high temperature, corrosive chemicals, explosive materials and slurry installations. A perfect solution for applications that can't be handled by floats or tanks "pitted in the ground" without access to mount pressure sensor.

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C

CE Rating:

This standard focuses on protecting the consumer. CE certification has to be done on products in their FINAL form as they will be used by the consumer. The example that best illustrates this is CE testing a motor in a dishwasher. The motor, standing alone in the CE lab may not pass the CE specifications because it isn't enclosed in the dishwasher cabinet. However, the entire dishwasher and motor can easily pass CE certification. The DistaView® controllers are similar to the motor. CE won't test the controllers in a "stand alone" condition. For testing to be undertaken the controller has to be mounted in the electrical enclosure with the voltage, components and conduit connections that will be delivered to the consumers. Since our controllers are "stand alone components" integrated into a wide variety of applications and manufacturing control systems it's not a certification we can receive. The CE testing and certification is ultimately the responsibility of the OEM selling the product.

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Control Points: (See Set Points in Glossary)

Cross Section of the Tank:

This is one of the patented features in all of the DistaView® controllers. The LED graphic bar can be set up to ONLY display the critical section or range within the total height of the tank. Similar to a subset, fraction or portion of something. Previous bar graphs simply showed zero, empty to 100% of the full sensor range. This limitation leads to significant confusion, misunderstand of the actual level in the tank or requires each sensor to be zeroed and spanned for each tank height and application.      For example in a municipal water tower with the sensor located at ground level you can now display ONLY the top 20 feet of the tower where t the reservoir is located rather than the entire stand pipe and reservoir. Typically the critical cross section displayed on the LED Bar Graph is slightly higher and lower than the High and Low Alarm levels.
(See Cross Section Using LiquaVision®.)

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Please read the Cross Section of the Tank glossary description above for a broader overview. This is the lowest level you will be able to see displayed by the LED Bar Graph. The low level is indicated by three small numbers located right below the LED Bar Graph. This number represents no control functions on LiquaVision® or TwoView®. It's a "housekeeping" or visual presentation function. If the green LED bar, indicating the actual level, doesn't appear on the LED Bar Graph it doesn't mean the controller has failed. The large numeric Actual Level display always provides you an accurate reading of what's happening in the tank or application even though it is less than the level set for the Lower Limit of Display Window. NOTE: 2Point® may use this number as a Low Alarm Level with some DIP Switch configurations.

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Upper Limit of Display Window:

Please read the Cross Section of the Tank glossary description above for a broader overview. This is the highest level you will be able to see displayed by the LED Bar Graph. The upper level is indicated by three small numbers located right above the LED Bar Graph. This number represents no control functions on LiquaVision® or TwoView®. It's a "housekeeping" or visual presentation function. If the green LED bar, indicating the actual level, completely fills the entire LED Bar Graph it doesn't mean the controller has failed. The large numeric Actual Level display always provides you an accurate reading of what's happening in the tank or application even though it is higher than the level set for the Upper Limit of Display Window. NOTE: 2Point® may use this number as a High Alarm Level with some DIP Switch configurations.

 

D

 

Data Logger:

With any analog signal, such as a 4-20mA used by the DistaView® product line, it's possible to automatically record what the level, temperature, pressure etc. is at any time and date. A data logger is wired in series with the 4-20mA signal and is set up to record the sensor activity every second, minute, 10 minutes etc. You choose and intervals to record the activity on a computer whenever you'd like. The recorded activity is downloaded into a computer at your location and is presented as a graph, spread sheet or a long list of text. It becomes your historical record to monitor performance, overflow, chemical usage temperature etc.
(See DistaLogger 8)

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Differential Relay:

The actual relay itself is not differential or discrete. It's a typical Form 'C' or Form 'A' relay mounted to the controllers circuit board. The term differential relay refers to how the controller operates the relay. For example in a Make Up application, when the level FALLS or DECREASES to a programmed set point the controller will CLOSE or activate the relay. Closing the relay completes the electrical circuit of the pump or valve and the tank is refilled. During refilling the DistaView® controller has internally "latched" the relay closed and continues holding it closed until the Make Up OFF level you programmed is reached. At that level the same relay is "unlatched", the electrical circuit is OPEN and the tank stops filling. The crucial thing to keep in mind is that the same relay is turning the pump or valve ON and OFF. The distance or difference between the ON and OFF level is why the term differential relay is used.
(See Set Points / Make Up Range & Sump Range in the Glossary for more information.)

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DIN Rail Mounted Terminals:

Inside the electrical enclosure is another set or wire terminals similar to the Phoenix Connector plugs on the side of the controller. Each wire that's connected to the controller is attached to another screw terminal mounted on the back panel inside the enclosure. The terminal are arranged side by side which are attached to a metal DIN Rail. The DIN rail holds all the terminals next to each other like they are a multiple wire plug but still allows wire terminals to be inserted or removed. This type of arrangement or interface is used to accommodate larger wire sizes or to jumper multiple wires together. It also relieves the mechanical stress and "jumble" sometimes caused by wiring the pump or alarms directly to the Phoenix controller plug(s).

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DIP Switch Configurations:

In the real world a DIP switch is a quick and easy way of rewiring the electrical connections on the circuit board. In relation to the DistaView product line it is how you allow or restrict access to programming certain functions. On LiquaVision the DIP switch provides three levels of access for changing programmed information such as levels and sensor range. The TwoView DIP switch controls security levels, assigns the primary pump and enables lead and lag pump alternation if desired. The 2Point DIP switch changes the security features and provides seven different ways to control the relays.
(See 2Point Level Controller for more information.)

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Discrete Relay:

The actual relay is not discrete or differential. It's a typical Form 'C' or Form 'A' relay mounted to the circuit board in the controller. The term discrete relay refers to how the controller operates the relay. For example a High Alarm relay in a controller: This is a discrete relay that is activated or closes when a RISING level occurs. As the level in the tank or application rises and equals the programmed High Alarm set point the controller switches the relay from its Normally Open condition to a Closed position. Typically when the relay switches to the Closed position the connected device, a horn or warning light will begin operating. It will continue to operate as long as the level is ABOVE the set point. As soon as the level falls below the High Alarm set point the relay returns to the Normally Open condition and the alarm horn turns off. Another way to describe a discrete relay is that there is only one level that turns the relay On & Off rather than a wide range between the On & Off levels that is seen using a differential relay in a Make Up or Sump application.

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Dry Contact or Dry Closure:

There never will be 120VAC, 24VDC or 220VAC coming from the DistaView control relays if there are no wires attached to the Phoenix connector. Power to operate anything attached to the terminal strip has to be provided from a separate source somewhere in the pump or alarm electrical circuit. This is why it's referred to as a dry closure or dry contact. NOTE: This is NOT the case in regards to the 4-20mA sensor circuit which does have at least 24VDC available for loop powering the sensor if desired.

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E

EEPROM:

This is where the actual operating instructions and programmed sensor range, offset and level information is "written" and stored inside the controller. Similar to word processing software used on a computer. Instructions for the relays and display items are recorded and stored each time they are programmed or changed. The central processing chip on the circuit board constantly refers to the EEPROM instructions and set point levels to operate the pumps, alarms and LED displays on the front of the controller.

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Endress + Hauser:

They manufacture an extensive line of process sensors. DistaView uses their PMC 131 and PMC 41 pressure sensors and ultrasonic ProSonic T as a mainstay for most liquid level applications.

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ERROR 1:

A fatal error has occurred within the controller and it must be replaced. You can try to power the unit down and repower it but that is not likely to fix this condition.

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ERROR 2:

A fatal error has occurred within the controller and it must be replaced. You can try to power the unit down and repower it but that is not likely to fix this condition.

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ERROR 3:

This indicates that there is less than 3.97mA* coming from the 4-20mA sensor. This condition can be cause by a failed sensor, improper wiring on the sensor connector plug the controller, a sensor that has drifted out of factory specifications or some of the components on the circuit board have failed because of improper wiring, a short in the sensor or any other type of outside electrical surge. When this condition exists the numeric display flashes ERR3 and the entire LED Bar Graph blinks. All of the relays default to their Normally Open conditions.
 *LiquaVision and TwoView have a small window between 4.0mA and 3.97mA's that displays an up /\ or down \/ "carrot" in front of a random number in the Actual Level numeric display. If the signal falls below 3.97mA's the ERR3 will appear. This warns the customer that the sensor is slightly out of calibration. It also can be used to set up probes and ultrasonic sensors without repeatedly filling and emptying the entire tank.
     To "fix" this condition the first thing to try is removing the main power going to the controller and plugging it in again to power up the controller. Secondly, check that the wiring throughout the sensor circuit is still in tact and has not been accidently changed by someone. Also check and see if there is actually liquid, pressure or vacuum present on the sensor. Occasionally the sensor will "drift" over time and not be producing 4.0mA in an "empty" situation. If none of these correct the error you are pretty much out of luck. Try wiring in another sensor to verify that the sensor circuit board is still operating. If that fails you will need to replace the controller.

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F

Fault Level:

This is a term usually refereed to when a high or low alarm level is reached.

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Flow Control / Bubbler Air Supply:

Adjustable Flow Control - In the bubbler system it's helpful to reduce the air flow going to the bubbler tube to a relatively low rate. Usually a rate of one cubic foot of air per hour or less is fine. In most of the existing bubbler systems there is an adjustable flow regulator that has a small bead that is kept floating in a calibrated clear plastic tube by the amount of air flow passing through the calibrated tube. By adjusting the needle valve at the input of the regulator the flow rate can be increased or decreased. The drawback to an adjustable air flow regulator is that the flow of air can be turned off making the bubbler useless. It can also be set very high which may give an artificially high level because the system is internally overpressured.

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Fixed Flow Control:

To avoid the drawbacks inherent in an adjustable flow control regulator DistaView uses a fixed flow control in their No Foolin' Around Bubbler. It is a fixed sized orifice that is calibrated to provide the required flow rate for the sensor and material being measured in the application.

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Form 'A' Relay:

The relay has only one set of contacts or one possible electrical circuit inside the relay that can control devices such as pumps and alarms. In the normal operating position the small coil inside the relay that controls the contacts position isn't energized. It's in a resting or sleeping mode. When a signal comes from the controller to activate one of the connected pumps or alarms the circuit board energizes the relay coil with a small amount of voltage and the coil "pulls in". It literally moves a set of contacts inside the relay from the Open or resting position to the Closed position which completes the circuit and turns on the pump or alarm. When the controller removes the voltage from the coil the contacts inside the relay return to the resting or Open position which turns off the pump or alarm. NOTE: There never will be 120VAC, 24VDC or 220VAC coming from the DistaView controller relays unless it's provided from an external source in the pump or alarm circuit(s). This is why it's referred to as a dry closure or dry contact. However, this is NOT the case in regards to the 4-20mA sensor circuit which always has at least 24VDC available for loop powering the sensor if desired.

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Form 'C' Relay:

The relay has two sets of contacts or two possible electrical circuits inside the relay. By moving the set of contacts from one position to another inside the relay the required operation of the pumps and alarms is achieved. In the normal operating position the coil that controls the position of the contacts inside the relay isn't energized. Typically the pump or alarm is NOT wired to this set of contacts because it would run all the time until the relay coil was energized, the contacts move the other position and interrupt the electrical pump circuit. Normally, when a signal comes from the controller to activate one of the connected pumps or alarms the circuit board turns on the relay coil with a small amount of voltage. That energizes the coil and it "pulls in", literally moving a set of contacts inside the relay from the Open position to the Closed position. Now the other set of contacts complete the electrical circuit and the pump or alarm begins to operate. When the controller removes the voltage from the coil the contacts return to the other position and the circuit is Opened which turns off the pump or alarm. NOTE: There never will be 120VAC, 24VDC or 220VAC coming from the DistaView controller relays unless it's provided from an external source in the pump or alarm circuit(s). This is why it's referred to as a dry closure or dry contact. However, this is NOT the case in regards to the 4-20mA sensor circuit which always has at least 24VDC available for loop powering the sensor if desired.

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I

Isolated Sensor Connection:

The sensor input connection has at least 24VDC available to "loop power" the sensor so they don't require a separate outside power supply. The Isolated term means that neither of the 4-20mA input signals (#4. 4-20mA (-) & #3. 4-20mA (+) ) are connected to the ommon or chassis ground of the main power supply source. This allows other devices such as PLC's and SCADA systems can be added to the sensor circuit without special preparation or unexpected consequences.

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L

Lead & Lag Pumps:

It's important to remember that the term Lag Pump is always used in conjunction with a Lead pump. It refers to operating two pumps from the same controller. The TwoView controller typically has two separate pumps connected to it along with a High and Low Alarm device. For example, in a municipal water tower application there are at least two pumps that fill the reservoir at the top of the tower. This is called a Make Up application. Under normal water usage one pump is sufficient to refill the tank when it decrease to the LEAD PUMP ON level. Occasionally, because of increased water usage the level may continue to fall even though the LEAD Pump is running. The LEAD Pump is the first differential pump range activated by the controller. As the level continues to fall even though the LEAD Pump is running the second differential pump range, LAG PUMP ON, is reached. This causes the controller to turn on the second pump connected to the LAG Pump Relay terminals. Now both the Lead & Lag pumps are running and trying to refill the water reservoir at the top of the tower. As the water level rises high enough to meet the LAG PUMP OFF level the controller turns it off. The LEAD Pump continues filling the tank until the l level reaches the LEAD PUMP OFF level. When the tank is refilled the LEAD Pump turns off. Both pumps remain off until the tank level falls to the programmed LEAD PUMP ON Level and the cycle begins again. Most of the time the LAG Pump isn't required to help fill the tank and remains a back up pump.

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Level Controller:

It's any device or combination of components that automatically controls the level in an application. The difference between the term "controller" and "display" is in the operations of an external device such as a pump or alarm. A display is a passive gauge that shows what the activity is in the application. A controller usually displays the activity in the application and performs some type of "work" by turning on and off devices connected to it such as pumps and alarms.

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Loop Powered:

Any sensor, regardless of what type it is, has to receive around 24VDC power to operate correctly. This can be supplied by a separate power supply somewhere in the sensor circuit. It can be provided through the sensor connection terminals on the DistaView controller or an external power supply can be located anywhere along the senor circuit. It's important to keep in mind that all of the devices included in the sensor loop circuit have to be in series. Essentially that means the negative lead of one component has to be wired to the positive lead of the next one in the loop and so on until you get back to the power supply. If you're "foggy" on this wiring format please check with a DistaView technical rep or the sensor manufacture before "letting the smoke out" of one of the chips inside the controller by mistake.

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M

Make Up Range: (See Set Points / Make Up Range in Glossary)

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Make Up Unit: (See Set Points / Make Up Range in Glossary)

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N

NEMA Rating:

This is an industry standard rating the level of protection electrical enclosure provide the components inside during specific types of environmental conditions and chemical exposures. NEMA 4 has a higher level of protection than NEMA 12. NEMA 4 is for indoor and outdoor use, protects against dust, wind debris and water sprayed from a hose. NEMA 12 is used for indoors only and protects against dust, falling dirt and dripping noncorrosive liquids. NEMA 4X has the same physical protection as NEMA 4 with the added protection from corrosive materials. Typically this is a fiberglass enclosure.

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Non-Isolated Sensor Connection:

This type of configuration of the sensor wiring on the circuit board itself was used in the original LiquaVision design. Serial numbers under 2000 have the Non-Isolated sensor configuration and three (3) 0.60 amp relays. The sensor input connection has the same 24VDC available to "loop power" the sensor as the isolated version currently used. The loop power is available so an external power supply isn't necessary. The Non-Isolated term means that the 4-20mA negative (-) input signal, terminal #4 on LiquaVision and TwoView, is connected to the negative (-) side of the 24VDC sensor loop power supply. Other devices such as PLC's and SCADA systems can be included in the loop but consideration for the Non-isolated connection have to be taken.

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O

Offset:

A sensor only knows how much material is ABOVE it and every controller has to know how much material is BELOW the sensor. The controller adds the two heights together and displays the Actual Level of the tank or application. During the initial controller programming there are ONLY two critical pieces of information that have to be entered correctly. One is Offset and the other is Sensor Range. The Offset Distance is how far from the tank bottom is the sensor located. The "Offset Distance" has to be in the same units as the display will be showing. If the numeric display on the front of the controller is showing inches the offset distance has to be entered as inches. If the numeric display on the front of the controller is showing gallons the offset distance has to be entered in gallons. Keep in mind that whatever engineering units you are showing on the graphics text are the same units you need to enter for the sensor range, offset and all the set points. The sensor only knows how much pressure or weight is acting upon it, you need to convert that information into the correct units when programming the controller. (See the Worksheets for Converting display units)

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P

Phoenix Connectors:

Sometimes a picture really is worth a thousand words. The picture shows a typical Phoenix connector used on all the DistaView controllers. They are the terminal strips that snap on and off the soldered in connector on the circuit board. The snap off part of the connector has a separate screw terminal for each wire. This allows you to wire up all the connections and flush mount the controller in the enclosure at a latter date. It's also easy to remove the controller from the enclosure in the event you want pre-wire the system and then paint the equipment before final assembly and shipping.
Photohelic gauge - This is a type of control device that has been used in many of the bubbler systems currently operating in manufacturing plants. The solid state level sensors and controllers are replacing this type of mechanical control system. It is basically a mechanical gauge that relies on changes in air pressure to move the indicator needle across the calibrated dial. As the needle moves across the dial there are two "adjustable" photo diodes or light sensors for an on and off point. When the needle passes over one of the photo cells a relay is activated turning something on or off. A similar mechanical gauge is called a Magnehelic gauge and operates in much the same manner except it uses a magnetic switch rather than a phot sensor for the control points. In either case the changes in air pressure are created using the bubbler technique.

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R

Regulator:

This device is used to continually provide a supply of air at the required pressure by adjusting the regulator. If you need to have no more than 50 psi of air pressure entering a particular piece of equipment and all the available plant air is 100 psi you'd put a regulator between the 100 psi plant air source and the equipment needing 50 psi. Regardless of what the air pressure changes are the regulator will always deliver 50 psi, unless the main air source drops below 50 psi.

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S

Sensors:

4-20mA:

This is one of the most common types of signal produced by process control sensors. When a sensor is in contact with an actual process such as pressure, temperature or distance, the mechanical action is converted into an electrical signal measured in milliampere (mA). 4.0mA is the amount of electrical current produced when no external forces are acting on the sensor such as an empty tank. 20.0mA is the electrical signal produced when the sensor is experiencing the maximum range of activity such as a full tank. An important aspect to understand about all senors is what sensor range is required for each application. (See Range in the Glossary for more information.) All the DistaView controllers accept a 4-20mA signal from any type of sensor. NOTE: 4.0mA was chosen as the "empty" condition rather than 0.0mA so a broken wire in the sensor circuit won't produce the same electrical signal as an empty tank. (See ERROR 3 in the Glossary for more information on how LiquaVision and TwoView indicate a broken sensor wire or failed sensor.)

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2 Wire Device:

This is a term used for a sensor that receives its operating voltage from the controller connection instead of being externally powered by a separate supply.

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Isolated Sensor Connection:

The sensor input connection has 24VDC available to "loop power" the sensor so an additional external power supply isn't required. The Isolated term means that neither of the 4-20mA input signals, terminal #4 / 4-20mA (-) & terminal #3 / 4- 20mA (+) are connected to the common or chassis ground of the main power supply source. This allows other devices such as PLC's and SCADA systems can be added to the sensor circuit without special preparation or unexpected consequences.

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Non-Isolated Sensor Connection:

This type of configuration of the sensor wiring on the circuit board itself was used in the original LiquaVision design. Serial numbers under 2000 have the Non-Isolated sensor configuration and three (3) 0.60 amp relays. The sensor input connection has the same 24VDC available to "loop power" the sensor as the isolated version currently used. The loop power is available so an external power supply isn't necessary. The Non-Isolated term means that the 4-20mA negative (-) input signal, terminal #4 on LiquaVision and TwoView, is connected to the negative (-) side of the 24VDC sensor loop power supply. Other devices such as PLC's and SCADA systems can be included in the loop but consideration for the Non-isolated connection have to be taken.

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Pressure Sensor:

There are three basic types of pressure sensors. One is a direct contact sensor that is screwed into a 3/8" or 1/2" NPT threaded fitting somewhere below the expected Low Alarm Level in the tank. The weight of the water above the sensor presses on the transducer. It converts the weight or pressure into an electrical signal that is connected to the controller. Most applications allow the sensor to be screwed into a 'T' in a fill or drain pipe going to the tank. This avoids cutting a hole into the tank wall. The "wetted parts" that will actually make contact and become wet with the measured liquid are usually 316 Stainless. Another version is the submersible pressure sensor. It is the same as the pressure sensor described above but the electronic components and wires that connect it to the controller are sealed in a flexible, waterproof "jacket".
(See Submersible Sensor in the Glossary for more information.) The other type of pressure sensor is used with dry air, noncorrosive and nonexplosive gases. This is the type of sensor DistaView uses with their bubbler systems to measure the back pressure created in the bubble tube. This type of sensor is also used in HVAC applications and clean room filters. There is usually two ports on the sensor. Never block or seal over the remaining port when using this type of sensor. The other port acts as the exhaust side for the port being used. If the exhaust port is blocked the sensor isn't able to move freely and react to the subtle changes in pressure or vacuum. NOTE: None of these sensors works well in applications with a sealed or un-vented tank unless additional consideration are undertaken. Temperature is another consideration. The material being measured shouldn't be higher than 212 degrees F. There are accessories that can be put on the sensor to protect it from the heat.

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Submersible Pressure Sensors:

These are fundamentally the same as a direct contact pressure sensor. The difference is a submersible sensor is dropped directly into the liquid by a cable. The electronics and wiring are enclosed in a flexible, water proof 'jacket'. The sensing head makes direct contact with the liquid just like the threaded pressure sensor described above. This style is desirable if there is no opportunity to access the tank and screw in a sensor such as a sewage lift station that is below ground level.

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Transducer:

A component in the sensor that actually "touches" the applications process such as pressure, temperature, or vacuum and converts that mechanical action into an electrical signal. On some types of ultrasonic senors the transducer is separated from the "main" components of the sensor called the transmitter. However, in the real world the term transducer, transmitter and sensor are used i interchangeably.

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Transmitter:

This is the actual sensing device inside the Sensor or Transducer. The electrical signal created by the transducer is not in a usable form for a typical controller. The Transmitter is the additional circuits required to convert the original transducer electrical signal into a usable 4-20mA signal required for the controller to process. However, in the real world the term transducer, transmitter and sensor are used interchangeably.

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Ultrasonic:

This works on the same principle flying bats use to locate bugs and avoid obstructions. A pulse is sent out from the sensor head and the internal electronics "count" how long it takes for the pulse or echo to return. By knowing the distance or time it takes for a signal to return from an empty and full tank the sensor and calculate what the level currently is in the tank. NOTE: The main considerations when using an Ultrasonic sensor is the diameter of the tank in relation to the height. The cone shaped width of the pulse beam can't be wider than the inside tank diameter or it will bounce off the sides and never return "to be counted". There are different size beams to accommodate this possibility. Also fog, vapor, temperature and foam above the liquid have the same disruptive effect on the pulse returning to be counted. There could also be caustic vapors that are incompatible with the materials the sensing head is constructed from. The most interesting and not obvious limitation to using an ultrasonic sensor is for applications that require measuring level inside a tank that is under vacuum. No "air" in the tank means there is nothing to carry the pulses. A laser will work as far as a non-contact sensor or a pressure sensor can be modified to operate under these conditions. The standard Endress + Hauser Ultrasonic sensor has an operating temperature limit of 176 degrees F.

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Sensor Terminal:

In the catalog it refers to the removable 4 pin, Phoenix type connector located on the sensor input of the controller.

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Set Points:

The set points are the programmed "levels" you entered into the DistaView controller. Usually set points are in units like inches, feet, pounds or gallons. When the level in the application reaches a programmed set point, either upon rising or falling, it cause the relays to open or close. That activates the control devices you have connected such as a pump, alarm or valve.

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High Alarm:

This is a discrete relay that is activated by a RISING level. As the level in the application rises and is equal to the programmed High Alarm Set Point the relay will switch from a Normally Open condition to a Closed position. Typically when the relay switches to the closed position the connected device, a horn or warning light will begin to operate. As soon as the level falls below the High Alarm Set Point the relay will return to the Normally Open condition. The High Alarm must be set higher than the highest level in the Make-Up or Sump operating range unless you have a custom EEPROM installed in the controller.

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Low Alarm:

This is a discrete relay that is activated by a FALLING level. As the level in the application falls and is equal to the programmed Low Alarm Set Point the relay will switch from a Normally Open condition to a Closed position. Typically when the relay switches to the Closed position the connected device will begin to operate such as a warning light or horn. As soon as the level rises above the Low Alarm set point the relay will return to the Normally Open condition. The Low Alarm must be set lower than the lowest level in the Make-Up or Sump operating range unless you have a custom EEPROM installed.

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Make Up Range:

A typical Make Up application is when the liquid in a tank is "lost" because its being used in a manufacturing process or lost by evaporation and has to periodically be refilled or "made up". To accomplish a Make Up operation the DistaView controllers use a differential relay that is activated by a FALLING level in the tank. The crucial thing to keep in mind is that the same relay is going to turn the pump or valve ON and OFF. First you need to program the Make Up ON level where you want to begin refilling the tank with liquid. When the level FALLS or DECREASES to this point the controller will CLOSE or activate the relay and turn ON a pump or valve and begin refilling the tank. The DistaView controller has internally "latched" the relay closed and will continue holding it closed until the Make Up OFF level you programmed is reached and the tank stops filling. NOTE: The LQV units with serial numbers above 2000 have a duplicate Make Up Relay available at pins #1, 2 & 3. It operates at the same levels as pins #7, 8 & 9. (See Programming LiquaVision or TwoView literature for more details.)

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Sump Range:

A typical Sump application is when the liquid in a tank is being collected and has to periodically be transferred or pumped out to prevent an overflow. A basement with a sump pump is doing the same type of operation. To accomplish this Sump Operation the DistaView controllers use a differential relay that is activated by a RISING level in the tank. The crucial thing to keep in mind is that the same relay is going to turn the pump or  valve ON and OFF. First you need to program the SUMP ON level where you want to begin draining the liquid i in the tank. When the level RISES or INCREASES to this level the controller will CLOSE or activate the relay and turn on a pump or valve and begin draining the tank. The DistaView controller has internally "latched" the relay closed and will continue holding it closed until the Sump OFF level you programmed is reached and the tank stops draining. NOTE: The LQV units with serial numbers above 2000 have a duplicate Sump Relay available at pins #1, 2 & 3. It operates at the same levels as pins #7,8 & 9.
(See Programming LiquaVision or TwoView literature for more details.)

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Sump Units: (See Sump Range in Glossary above)

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Surge Suppressor:

This is critical protection for the relays on all of the DistaView controllers. There is protection designed into the controller circuits but additional suppression should be used for large devices such as motors, solenoids and starters. This is called a lot of things in industry - snubber, RC Network, reverse diode and a resistive/ capacitor device. On AC devices you use a RC Network type of device and on DC devices such as solenoids use a reverse diode arrangement. It protects the relay coils on the DistaView circuit board from being damaged by a very high surge or "inrush" voltage when a coil or motor is operated. Surge suppressors connect across the terminals of the inductive load such as a coil, solenoid or motor starter.

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T

Terminal Strip:

Sometimes a picture really is worth a thousand words. The picture shows a typical Phoenix connector used on all the DistaView controllers. This is a term referring to any type of connector or plug that wire(s) are attached to. In the DistaView product line all of the controllers use a snap on "Phoenix" type connector for the power, control devices and sensor input. The snap on part of the terminal connector has a screw to secure each wire on the plug.

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Transducer Location: (See Offset in Glossary)

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Transducer Range or Sensor Range:

This is the most important and most misunderstood concept in the entire catalog. A dangerous combination don't you think? Without a clear understanding of Sensor Range it's improbable a reliable level control system will be installed. There is only one thing to understand about sensor range, and only one thing - the range is decided by the manufacture when the sensor is made. There is nothing you can change, program or measure that will change it. The sensor range has to be decided before it is ordered and it has to be matched to the height or amount of material it will be measuring.
      Another analogy can be used by comparing sensor range to camera film speed. Camera film is manufactured with speeds of 100, 200 or 400 ASA. You choose a particular film speed to match the type of light or activity to be photographed. You can't change the film speed nor do you want to. The only thing the camera needs to know when you load the film is - what's the speed of the film you just put it. If that's correct you can adjust the shutter speed and lens opening to enhance the cameras capabilities and get the exact photographs you'd hoped for. That's the same thing the DistaView controllers want to know - what is the range of the senor that's going to be  sending me information. Once it knows that and whereit's mounted inside the tank it can provide accurate and reliable display and control.
      To determine the correct sensor range the first consideration is what the overall height or distance that is going to be ABOVE the sensor location. This is important because if you have a 300 foot deep outdoor reservoir and only need to "control" the top 2 - 3 foot the sensor range could be as low as 3 feet. It makes it a lot easier to mount a sensor 3 feet underwater instead of 300 feet under. If the level won't drop more than 3 feet than this sensor range will work. The Offset level for this application will have to be 297 feet to give you accurate display information.

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V

Vacuum Application:

Usually a manufacturing process has fluids or air travelling inside the equipment that are under pressure. However, in many applications the air or fluids can be under vacuum which is less that the normal air pressure we experience every day. One that comes to mind is a process called de-airing. When viscous liquids are mixed air is trapped inside. To remove the trapped air the liquid can be placed in an air tight chamber.

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