Selling a service is selling the intangible. You know, as a consumer, if you are getting great service from a business. You can feel it, but sometimes it’s hard to actually define. Many times, listening to a demand, a complaint, or a request is all that’s needed to provide great service. In product management circles, Voice of the Customer (VoC) is one of the most important drivers in product development. If we LISTEN really well, the solution has already been provided for us. If a customer says, “I wish you had a widget that would do this.” Or “I need a product to do this for me”.   When you hear those statements, LISTEN, and take good notes.

Ascertaining VoC can be a challenge for many companies. How can you systemically listen to thousands of “I wish” or “I need” statements and boil it down to a working product development list? At Kele we actually utilize a very modern marketing department to help cultivate customer responses and needs. Using digital media and short surveys gives the product management team at Kele a gateway to thousands of customer voices and opinions. We sort through them quickly and this VoC gives us solutions to provide better products and better services to you the consumer. Of course it takes your participation in the surveys and you, our customer base, have been great about providing your preferences.

One example, is the Kele Water Detector (WD) family expansion project that is launching at the 2016 AHR Expo in Orlando. Kele has provided a legacy water detector device for over 20 years, and continues to serve a wide range of customers. We started to get “I Wish” responses from WD users like this:

I really like your WD product but I WISH you had a poly material (plastic) enclosure option.

I WISH it had a cable option that could bend around corners in the long sensor run.

We literally sorted through hundreds of survey responses. This form of VoC (your responses) helped shape the design requirements for the next generation of Kele water detectors. Our offering has expanded significantly. We also understood through VoC that our legacy WD product is a great product, and is still required by the industry. So many times, product launches involve a planned obsolescence of existing part numbers. In this case customers spoke, no obsolescence is planned, only expansion of a strong product legacy. So thank you for the feedback, we will continue to provide great customer service, and LISTEN.

Current transformers (CT) are simple and reliable devices which make it possible to make accurate measurements of alternating current flowing in a conductor without making any electrical contact. This characteristic makes the current transformer, or CT an invaluable tool for the power utility industry.

The principle of operation of a CT is the sensing of the magnetomotive force around a current-carrying conductor. The CT contains a high permeability magnetic core, and a multiple turn secondary winding. This secondary winding links all the magnetic flux generated in the core by the magnetomotive force (mmf) caused by the current in the primary conductor.

The CT therefore resembles other transformers. The goal in designing a CT is to approach the behavior of an ideal transformer, where the permeability of the core can be considered infinite; the resistance of the windings is zero, and both windings link exactly the same magnetic flux. To the extent these conditions are met, the transformer will have two properties:

1. The voltage per turn will be equal on both the primary and the secondary
   windings, so that the ratio V (sec)/V (pri) = N (sec)/N (pri).
2. The net magnetizing current is zero, so I (pri) x N(pri) + I (sec) x N (sec)=0, or I (sec)/N(pri)= -I (pri)/N(sec)

A 4-20 mA control signal is one of the signals of choice in the Building Automation industry as well as in the Industrial Process arena. Most of the various transmitters and output devices available from Kele utilize a 4-20 mA input or output signal. In large commercial buildings, expansive factories, multi-building university campuses and other large projects, it is not unusual to find an application where a transmitter is located a long distance from the nearest building automation controller. We are frequently asked, “How far can 4-20 mA signal wires be run?”. The answer is quite amazing.

A 4-20 mA current loop consists of a number of devices wired in a series loop. These devices include a power supply, a sensor/transmitter and one or more loads such as a building automation input, a chart recorder, an alarm module or a digital display. Depending on the type of transmitter used, the power supply may either power the transmitter external to the loop or the power supply may be one of the devices in the series loop as shown in Figure 1.

The transmitter is a 4-20 mA current source that requires a DC voltage supply to operate. The transmitter in Figure 1 is a model PTX1 pressure transmitter. Reviewing the PTX1’s specifications in the Kele catalog shows that it can operate with a power supply voltage from 10 to 30 VDC. However, the actual power supply voltage used will directly affect the output capability of the transmitter. To provide its full output, the transmitter must be capable of supporting the total resistance of all loads that are wired in the loop. Again looking to the specifications of the PTX1, there is a graph (Figure 2) that indicates the output load capabilities of the PTX1 for supply voltages from 10 to 30 VDC.

A quick study of the graph shows that when using a 10 VDC power supply, the PTX1 can support a maximum load of zero ohms! In other words, the PTX1 requires 10 VDC just to power its internal electronics (power supply overhead). For the transmitter to drive its 4-20 mA signal through any load at all, the power supply must be increased above the 10 VDC overhead required by the PTX1. As indicated by the graph, a 30 VDC supply will allow the transmitter to handle over 900 ohms of load in the loop. At 24 VDC the transmitter is rated for 650 ohms.

Looking back to Figure 1 shows that the building automation input is 250 ohms and the chart recorder adds 250 ohms. The total load of 500 ohms is within the 650 ohm capability of the PTX1 with a 24 VDC supply.

So what does all of this have to do with how far 4-20 mA signal wires can be run? There is an additional load on the loop that has not yet been considered. This additional load is the resistance of the wiring connecting the devices in the loop. For shorter signal wiring runs the resistance added by the wire is negligible, but what effect will long wiring distances have on the loop? By considering the wiring resistance as an additional load, the allowable length of wiring in the loop can be determined.

In Figure 3 the loop is powered by 24 VDC which means the PTX1 can drive its 4-20 mA output into a maximum of 650 ohms. The distance from the control panel to the PTX1 transmitter is 1000 feet and is to be wired with 18 gauge wire. The resistance of 18 gauge wire is 0.00651 ohms per foot. The total resistance of the wire in the loop, Rw x 2, is 13.02 ohms (1000 ft x 0.00651 ohms/ft x 2 = 13.02 ohms). The total resistance of the loop then is 513.02 ohms, which includes the resistance of the wiring added to the building automation input and chart recorder. In the real world, additional resistance may be added to the actual total loop resistance by wiring connection points such as terminal blocks, splices, etc. The total loop resistance of 513.02 ohms is less than the maximum output rating of 650 ohms so the PTX1 will work in this application.

The amazing part is to do the math to determine the maximum allowable wiring distance for the example in Figure 3.

Even with two loads (500 ohms), a building automation input and a chart recorder, the signal wiring from the control panel to the PTX1 transmitter could be as long as 11,520 feet or more than 2 miles! The characteristics of the PTX1 are not unique. Kele has 4-20 mA transmitters available to handle loads from 300 to over 1000 ohms.

 Of course, there are additional factors to consider when running signal wiring over a long or even short distance. These factors include protecting against the effects of radio frequency interference (RFI) and electromagnetic interference (EMI) by never running signal wires in the same conduit as AC power lines, considering the use of shielded twisted wires, employing surge protection when running between buildings, and always following national and local electrical codes.

Remember, when you face a long signal wiring run, a 4-20 mA transmitter from Kele will go the distance.

Reprinted from Winter 1996 Kele Insights

Kele designed the Universal Flow Transmitter (UFT) for use with Badger/Data Industrial flow sensors, but in reality the UFT can be used with many other makes and models of flow sensors if their signal outputs are compatible with the UFT signal input.

Kele frequently gets asked the question “will this Model XYZ flow sensor work with the UFT?”  So we decided that it might be a good idea to write an article addressing this topic and at the same time provide other application information beyond that shown on the UFT data sheet.

UFT Power

The UFT requires 24VDC +/- 10% at 80 mA maximum for operation.  Note that the UFT cannot be powered with 24VAC.

UFT Flow Sensor Input Circuit

The UFT will accept pulses from the following types of flow sensors:

1. Sensor output that is open-circuit in the “high” state and conducts to common in the “low” state.  Most Badger/Data Industrial flow sensors operate this way.  For this type of sensor output, install the “PWR XDCR” jumper located near the PWR LED across both pins of the header.  When the sensor contact is open, 8V will appear across it.  When the sensor contact is closed, 8 mA of current will flow through it.

   

    

2. Powered sensor output that drives to a “high” value of +5 to +24VDC and drives to a “low” value of 0 to +2VDC.  For this type of sensor install the PWR XDCR jumper on just one pin of the 2-pin header.

   

Up to 2000 feet of sensor cable 20AWG or larger can be used with the UFT, but to reduce noise pickup, please use the shortest length of sensor cable actually needed for the application.

The flow sensor must put out no pulses (0 Hertz signal) with no flow.

To be compatible with the UFT Span adjustment range, the flow sensor must put out pulses between 15 Hertz and 150 Hertz at full flow velocity (max GPM).

There is an XCDR SIG IN LED that indicates the state of the input signal from the flow sensor.  When the input is “high” the LED is on, when the input is “low” the LED is off.  When the pulse rate is fast, the LED may appear to stay on continuously even though it is actually going on and off very rapidly.  If the sensor is working properly, you should always be able to see the LED flashing when the flow is first starting up or ramping back down to zero.  At no flow, the XDCR SIG IN LED may be either on or off depending on the resting state of the flow sensor output.

The UFT can be factory modified to handle higher input frequencies (up to 1000 Hertz) at max flow velocity.  It cannot be modified to handle any frequency lower than 15 Hertz at max flow velocity.

4-20 mA Output Circuit

The 4-20 mA output represents the instantaneous (averaged over about 5 seconds) flow rate.  The UFT powers (sources) the 4-20 mA internally, an external power supply should not be inserted in the 4-20 mA loop.  The output will be 4 mA at 0 GPM (no flow).  The output will be 20 mA at whatever maximum flow GPM the UFT is calibrated for.

The 4-20 mA output is designed to drive a maximum load impedance of 750 ohms.  If the mA output is open-circuited, approximately 20V will appear between MA SIG OUT and COMMON.

The 4-20 mA output normally comes from Kele pre-calibrated for the sensor model and maximum flow rate specified on the customer order.  When Kele calibrates the UFT, a label is attached to the top of the board specifying the calibration parameters. 

Field Calibration (Not Recommended)

The UFT can be field calibrated if a steady maximum flow rate can be maintained (see following procedure).

Caution:  once the SPAN pot is turned in the field, it will be impossible to fall back to the factory calibration setting that was done at Kele.

1. Stop flow completely (or disconnect sensor wire) and trim the ZERO pot for 4 mA output.
2. Establish steady max flow rate and trim SPAN pot for 20 mA output.

The 4-20 mA output changes slowly when trimming the ZERO and SPAN pots, you must be patient and wait for the output to stop changing with each pot adjustment.

Pulse Output Circuit

The UFT pulse output circuit can be used to drive a mechanical/electronic totalizer or an automation system binary input point for gallon totalization in software.

The UFT pulse output is optically isolated from the remaining UFT electronics.  The pulse output does not drive any voltage of its own, the voltage must be provided by the load.  The pulse output connections are polarity sensitive.

In the “high” state the pulse output is open-circuit.  In the “low” state the plus and minus terminals are connected together with approximately a 0.7V difference between them.  This will be seen by most automation system binary inputs as a contact closure. The UFT pulse output can operate from 1-40VDC in the “high” (open) state.  The UFT pulse output can carry as much as 200 mA in the “low” state

The pulse output is jumper-selectable for divide-by-10 or divide-by-100 operation.  For divide-by-10 operation, one complete (high and low) output pulse is generated for each 10 sensor pulses.  For divide-by-100 operation, one complete (high and low) output pulse is generated for each 100 sensor pulses.  There is no other calibration for the UFT pulse output (no trimpots). There is a PULSE OUT LED which indicates whether the pulse output is open-circuit (LED off) or conducting (LED on).  Note that if the pulses stop coming from the flow sensor, the output could stop in either the open-circuit (LED off) or conducting (LED on) state.

Testing the UFT Without a Flow Sensor

1. Disconnect the sensor wire (if present) from the XDCR SIGNAL IN screw.
2. Install the PWR XDCR jumper on both header posts.
3. Move the divide-by-10/100 jumper to the 10 position.
4. Connect a jumper wire to the Common screw.
5. Tap the other end of the jumper wire on the XDCR SIGNAL IN screw.

As you tap the wire, you should see the XDCR SIG IN LED go on and off.  The PULSE OUT LED should cycle on and off for every few taps of the wire.  The mA signal should rise above 4 mA and the faster you tap, the higher the mA should go. If the UFT behaves as described above, it is functioning properly.