Two Wire Transmitters

Some People Like

Trimpots!

We recently picked up a new customer who ordered a few of our 2-wire thermocouple transmitters. This customer sells thermocouples and other temperature probes, and the manufacturer they represent also offers transmitters from a well-knows European company.

Why did they buy ours? The European brand is computer-ranged. The end user wanted to be able to adjust calibration without needing a computer set-up. So, they bought our "old fashion analog" fixed range Model JH220 - complete with trimpots!

This is at least the second time this has happened. Another of our customers, a temperature sensor manufacturer, ran into exactly the same objection years ago and regularly offers our transmitters even though they also handle the European brand.

Do you need to change ranges but still like trimpots? Model JH225 (shown) adds switches that let you recalibrate to almost any practical range for thermocouple types J, K and T. (You do need a calibration source.) We also offer similar transmitters for RTD (resistance thermometer) sensors.

Links:
Model JH220, thermocouple 2-wire transmitter, fixed range (factory set)
Model JH225, thermocouple 2-wire transmitter, user-rangeable
Model JH240, RTD (resistance thermometer) 2-wire transmitter, fixed range
Model JH245, RTD 2-wire transmitter, user-rangeable

All 2-Wire Transmitters

Product Spotlight

Two-Wire Transmitter -

Potentiometer Input

Our "sleeper" product - not new and, you would think, not particularly exciting, but people keep finding it and buying it, so we thought we'd feature it.

Pretty simple - takes a potentiometer input and converts it to a 4-20mA two-wire (loop-powered) output. Quite honestly, it was an afterthought when we designed our temperature (RTD and thermocouple) two wire transmitters years ago. Laying out the circuit board so it could also be assembled for potentiometer input was easy, so we included it.

Sells better than we ever expected. Just this month we picked up two new customers for it. The applications can be anything that needs to convert position to an electrical signal. A couple applications - level measurement and boat throttle position. The level measurement application uses a probe with series of resistors and reed switches, activated by a magnetic float.

Links: Model JH250 Potentiometer Transmitter
Other Two-Wire Transmitters
Our web site - http://www.jhtechnology.com/

Simple Specials

CUSTOM

MODIFICATION:

TWO INPUT RANGES

Our OEM customer, who manufactures level control systems, wanted to be able to interface more than one type of level sensor with his system. Specifically, he needed to translate both 4/20mA and 0/5 volt level signals to match his system's input.

Our solution - a modified version of our JH4300 DC Input Transmitter capable of accepting both ranges. For 4/20mA the input is connected to pins 5 & 6. For 0/5 volts pins 4 & 6 are used, plus a jumper between two terminals. This avoids the need to stock two different types of signal conditioners.

More detail. Their level system normally uses a variable resistance level sensor. (In fact, they are a regular customer for our resistance input transmitters.) 4/20mA or 0/5V is only occasionally required, so they did not wish to redesign the system's electronics. Their original request was, could we translate 4/20mA or 0/5 volts to a 0/90 ohm resistance? The answer was no, this would not be a simple modification.

Instead, they determined and we verified that their electronics passes a constant 2.5 mAdc current through the sensor. Thus, 0/90 ohms translates to 0/0.225 volts. We set up our output for this range.

Conclusion: they now are able to work with several types of level sensors without modifying their system. All they need to do is connect the level sensor to our module and connect the JH4300's output to their system's input.

If you have similar needs, please remember that we can make "simple" modifications without large engineering costs or minimum order requirements. To contact us e-mail jhtek@jhtechnology.com or phone (800) 808-0300 (outside the US, 941-927-0300).

Links: Custom & Special Process Transmitters
JH Technology Web Site: http://www.jhtechnology.com/

Absolute Value Function

Absolute Value -

with a difference

(Details on the application mentioned in our September 27 posting.)

A new customer had an urgent need for a signal conditioner (transmitter) with absolute value response. Searching the internet, he read our "Specials & Customs" page and found that we had done this before. His need was different, but we were able to help him.

For those of you who may not be familiar with the absolute value function, it simply ignores the minus sign. The previous special which he found on our web site took a -10 to +10 volt input and created a proportional 0 to +10V output. For example, inputs of either minus 7V or plus 7V created a plus 7V output.

The new customer's application needed a signal representing the temperature deviation from ideal. Ideal temperature produced a 12mA current signal. A deviation, whether positive or negative, required a positive-going output (see graph). At 12mA input the output should be zero percent (4mA). At either 4mA and 20mA (8mA deviation) the output should be 20mA (100%).

We were able to modify the earlier special to accomplish this. As mentioned in our Sept. 27, 2009 post we did some Thursday evening calculations, quoted and took the order on Friday, built 6 units on Saturday (yes - we added an expediting charge) and shipped Monday.

Let us know what we can do for you!

Links: Custom & Special Signal Conditioners
Our home page: http://www.jhtechnology.com/

Split 4-20mA Loops without a Loop Splitter

Save money! Don't buy a loop splitter if you don't need one.

Users often specify dual-output 4-2omA current loop splitters in their systems. Common reasons include:

• The need for an output boost to drive several loads at once.


• The need to run independent isolated current loops to two different systems.
  

These needs often can be met with a less-expensive single-loop isolator. The diagram shows the basic idea - use the source transmitter to drive the isolator's input plus the first loop, then use the isolator's output to drive the second loop.
















For our complete application note (pdf) click here , or visit http://www.jhtechnology.com/ and click on the Application Notes link.