Signal Isolator Serves as Subtractor

Measurement and control applications sometimes need a difference (A - B) calculation. Examples include:

• Liquid level measurement in a closed vessel. Level is proportional to the bottom liquid pressure minus the top ambient (gas or air) pressure.
• Liquid blending control. Must maintain a zero difference between two measured flow rates.
• Relative speed control. Control for zero difference between two speed measurements.

JH Technology offers a complete range of multiple input add/subtract instruments, but when the inputs are voltages a lower-cost isolator may do the job.
The figure shows two voltages, both grounded. The signals may come from two pressure or flow transmitters, tachometers or other sources. The isolator's input is connected between the two positive voltages; thus, the input is (V1 - V2). Its output may be set to equal the differential input or it may be scaled up or down, offset or converted to a current signal such as 4-20mA.
We offer plug-in, DIN rail and field mount style isolators and transmitters.

Links: Add/Subtract Transmitter Modules
DIN-Rail style add/subtract transmitters
All Process Transmitters and Alarms

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/

Just for Fun - Hallowe'en 2009

HAPPY HOLIDAYS!!!!!

Created by Rick Maccani, our Technical Services Manager - with help from his wife.

For those of you who are "electronically challenged" the symbols are - - eyes=diodes, nose= capacitor, mouth equals resistor.

Special Modifications

Rapid Increase, Slow Decrease

("Peak Picker")

We've done this for a few customers. The basic application - monitor the peak value of a repetitive signal.
The first application was on an automated machine which formed nail heads. We never saw the machine, but our understanding is that it would "whack" heads on the nails in rapid succession. The user needed to know and control the impact force - not each and every individual impact, but the "normal" or "average" impact. In other words, he needed to know that the machine was properly set.
As the sketch shows, the output rises quickly to the peak value but decays slowly. (Actually, the unit we built had more filtering than is shown in the illustration.) The output of our module smoothed and held the value of the peak impact force.
We've built a few variations on this theme. One had an adjustable decay time (reference - our special feature #X0098) and one had a fixed 3-second time constant (X0214). Right now we're quoting a unit which adds a polarity-insensitive "absolute value" function - both positive and negative peaks will produce a positive output.

Links: Custom & Special Signal Conditioners
Our complete signal conditioner line

Special Modifications

Slow Increase, Rapid Decrease

Just the opposite of the "peak picker".

Application - Heating oven control.
The customer wanted to avoid rapid temperature increases and overheating and so wanted a "slow" filter on the control input. On the other hand, he required a rapid turn-off for fast shutdown. We were able to modify our transmitter's input stage to accomplish this.
(Reference - our special feature #X0251.)

Links: Special & Custom Signal Conditioners
Our complete signal conditioner line

New Product - Pulse Amplifiers

New Product

Announcement -

Low-Cost

Pulse Amplifiers

We've added two new pulse amplifiers to our product line.

For tachometers, turbine flowmeters and other magnetic coil pickups: Model JH376.

Two channels in one 0.7 in wide case. Each output is jumper-selectable, either 5V pulses or open collector. Highly sensitive, but includes sensitivity adjustments to optimize performance in noisy environments.

To convert logic pulses: Model JH377.

Inputs are jumper-selectable, either 5V/TTL or open-collector/contact closure. Outputs are jumper-selectable, either 5V pulses or open-collector. Again, two channels in one case.

Both products operate from 7 to 24Vdc power and at temperatures from -40 to +80 degrees C (-40 to 176 deg. F).

Links: Pulse Amplifiers and related products
All JH Technology Signal Conditioners

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/