Thermocouple Application Note

Unusual Thermocouple Application

Our customer's client had a large spa facility. The controls had been located near the spa, but the client felt they should be moved to a more benign environment, several hundred feet away. The system included four thermocouples. Sending thermocouple signals this distance is expensive, since thermocouple wire (not copper) must be used. Even more basic, sending weak millivolt signals hundreds of feet leaves them subject to interference and signal degradation.

To boost the signals, four standard thermocouple transmitters (our Model JH4130) were added near the spa. Their 4-20mA current signals easily traveled the distance with no degradation. The system designers opted not to change the control system, so it was necessary to convert the current signals back to their original thermocouple voltages. "Reverse" thermocouple transmitters, 4-20mA input, thermocouple output, were needed.

We provided them. We modified our Model JH4300 DC input, DC output transmitters to have the proper millivolt outputs. The most interesting challenge was, the millivolt outputs needed to be connected to thermocouple wires (not copper) for proper connection to the system's thermocouple inputs. This called for the reverse of cold junction compensation (we called it "cold junction un-compensation"). A temperature sensor embedded in the output terminals and some properly-designed circuitry solved the problem

Temperature Transmitters & Signal Conditioners - our web site: http://www.jhtechnology.com/

Application Note

AC to DC Translation Monitors Shaker Motion

Here's an application we did 10 years ago for a major manufacturer of membrane-based filtration equipment. They're still using it.

The need - to monitor and control filter movement. Motorized systems are used to oscillate large filter elements back and forth. Peak-to-peak motion is controlled using motor drives. Motion is continuously monitored using laser-based displacement (position) measurement equipment.

The problem – the laser’s output represents instantaneous position, varying continuously as the filter shakes back and forth. The company needed to convert peak-to-peak displacement to 4-20mAdc input current for the motor drive controllers.

The solution – our Model JH5600 AC Input Transmitter. Because the filters are large and driven by rotating equipment their motion is purely sinusoidal so the relationships between average, RMS and peak values are well known. In this application an input range of 0 to 3.536 volts RMS (odd ranges are not special for us) corresponds to 0 to 10 volts peak-to-peak. We have in the past created special modifications for true peak-to-peak measurement, but this was not required for this application

For those who prefer plug-in style modules, the same function is available in our Model JH6010I.

Click here for a link to a pdf of this application note.

AC Input Transmitters, Signal Conditioners - our web site: http://www.jhtechnology.com/
 
JH5600 data sheet: www.jhtechnology.com/dinrail_tx/jh5600_5610.htm

New Products

Integrators
(DC to Frequency Converters)

Brand-new Models JH7500 & JH7501 integrators convert a DC measurement signal (voltage or current) to a proportional frequency. JH7500 is the general-purpose version. JH7501 operates at low pulse rates - its output is a set of relay contacts that 'click' at the output pulse rate.

Integrator - why the name?

The original - and still common - application is to totalize, or "integrate" flow measurements. A signal from a flowmeter represents flow rate (such as gallons per minute). Each output pulse represents a fixed quantity (such as a gallon, fraction of a gallon or number of gallons). The pulses are fed to a counter. The faster the flow the faster the pulses, so the total flow may be found by reading the counter. Similarly, if the input represents instantaneous power (kilowatts) the total represents power usage (kilowatt-hours).

More modern applications include signal conversion (convert a DC measurement signal to frequency for a PLC's input) and tone telemetry (transmit the converted frequency over a distance, then convert it back to DC at the receiving eng. JH Technology offers frequency to DC converters (also called frequency input transmitters) to perform the receiving end conversion.

For product details click:
JH7500/JH7501 Integrators (DC to Frequency Converters
JH7010I Frequency to DC Converter (Plug-in style, fixed range)
JH7580 Frequency to DC Converter (Plug-in style, user rangeable)
JH5700 Frequency to DC Converter (DIN-rail style, fixed range)

Our web site: http://www.jhtechnology.com/

New from JH Technology

FAST Response!

Transmitters with 1 millisecond response time.

Last year we spotlighted a new design we'd done for a customer needing a quantity of fast-response transmitters. We've now turned it into a standard product offering.

Available on most of our DIN-rail transmitters (JH5000 Series), Option HS output is approximately complete (95% response) in 0.001 seconds. It is not available on AC input or frequency input transmitters, as these require filtering to function properly.

Frequency response is 3dB down (0.707 times the DC gain) at approximately 600 Hz.

Faster (or slower) available - contact us!

Link to Fast Response Process Transmitters

Signal Conditioners & Process Transmitters (link to our web site): www.jhtechnology.com/    

e-mail jhtek@jhtechnology.com

Custom Designs

A Very Special Special

A well-known company needed to duplicate a thermocouple alarm they had bought from Action Instruments decades ago. Action was no longer able to provide it so they turned to us.

Action's original "Action Pak" line (Action's trademark) once included alarm modules with extra options such as retransmitting outputs and remote setpoint inputs. 20-pin headers (pin bases) were required to provide the extra connections. As far as we are aware these headers are no longer available.

Our customer's requirement was a nonstandard version of one of those alarms. We replied that we could provide the same function but with a different connection arrangement. This was not acceptable - it was for a nuclear power application and they could not vary the system design. Only one piece, but they were willing to pay for it.

Once again we got lucky. In 1995 we had purchased some 20 pin headers for another customer's need and had a handful left. Our customer bought one (couldn't convince them to buy a spare) - even sent an inspector to Florida to do a source inspection. That was 2008. In 2009 they again bought one and just now ordered two more! Possible future problem - after this order we have only five headers left.

(Note: We do not sell nuclear-approved products. This alarm was sold as "standard commercial quality" for a noncritical application.)

Technical detail: the custom alarm module has two retransmitting 0-1V analog outputs, one proportional to temperature and the other proportional to the setpoint. Our customer was able to supply us with Action's specifications and we designed it to be functionally identical. Here's the functional diagram.

If you have special requirements let us know. Phone (941) 927-0300 or toll-free (800) 808-0300.

E-mail jhtek@jhtechnology.com.

Link to our page on Custom & Special Signal Conditioners.

Signal Conditioners, General - our web site: http://www.jhtechnology.com/

Economic Upturn?

Maybe. We're seeing signs.

After a best-ever 2008 we saw about a 25% downturn in 2009. 2010 started off equally bad, maybe even worse. Then, April & May were strong - above our 2008 average. We're cautious, though. The two months were helped by unusually large orders from four customers. So - cautiously optimistic!

Another sign - not necessarily good - component shortages and lead times are increasing rapidly - up to 20 weeks. So far we're able to cope, as most of our parts are available from multiple sources.

Such problems aside, let's hope the improvement continues.

Application Note

Detect Thermocouple Failure Without Upsetting the Process

One from the archives. Our customer needed to alarm on thermocouple failure without shutting down the process.

Thermocouple instruments commonly include upscale burnout indication. If the thermocouple breaks or fails open-circuit the instrument's output goes high, just as if the temperature had gone out of control. This often is used to insure failsafe failure, shutting the process down and sounding an alarm.

Our customer, a utility, needed an overtemperature shutdown on a monitored water temperature. They also wanted to trip an alarm upon thermocouple failure but without interrupting the process. We were able to suggest a simple dual-trip alarm setup to do this.

Our thermocouple instruments, like most others, offer a downscale burnout option. (Thermcouple failure causes the output to go low instead of high.) Using a dual-trip alarm, we set trip #1 for HI trip and trip #2 for LO. The HI trip, of course, was used to shut the process down on excessive temperature. The LO trip was set below freezing. Its relay would trip when the thermocouple failed but never under normal operation.

For the full application note, click here.

Our web site - Signal Conditioners, Process Transmitters: http://www.jhtechnology.com/

E-mail: jhtek@jhtechnology.com