True RMS Measurement Includes DC

Simple Modifications meet Customer's Needs

When measuring AC voltages, DC components or offsets usually should be ignored. Examples include measuring AC ripple from a DC power supply, and data or audio signals superimposed on DC power lines. As shown in the figure, a blocking capacitor removes any DC component.

Therm-O-Link, a wire manufacturer in El Paso, uses rectified but triac-modulated power in their annealing operation. To monitor and control the annealing process they need to know the total voltage, DC plus AC. They also need true-RMS measurement for accurate power monitoring regardless of the waveform.

A simple modification to our true-RMS process transmitter, Model JH6010IR, removed the blocking capacitor for full DC response. Additional changes speeded the transmitter's response time for proper operation in their control system.

For the complete application note, True RMS: AC or DC Response?, click here.

True RMS Measurement Basics

RMS measurements express the power capability of an AC source. Low-cost meters and transmitters often make a simpler average measurement rather than true RMS. The two are not the same, and the relationship between average and RMS measurements varies for different waveform shapes. The figure shows a pure sine wave, a chopped and rectified sine wave and a square wave pulse.

True RMS measurements require more complex and expensive circuitry, generally available in slightly higher priced instruments.

To learn the fundamentals of RMS measurement click for our application note, What is True RMS - and When do I Need It?


JH Technology manufactures:
Plug-In True RMS AC Process Transmitter
DIN Rail Mount True RMS AC Process Transmitter
Field Mound True RMS AC Transmitter with Display
Plug-In AC Alarm Trips with True RMS Response

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/

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/

Product Spotlight

Field-Mount

Transmitters

with Displays

Designed for outdoor and other wet/dirty environments, our FDT5000 series transmitters feature:

• Splashproof/ Corrosion Resistant Enclosure per NEMA 4X
• User-Rangeable 3-1/2 Digit Display
• Wide Selection of Input Styles
• Voltage or Current Output Ranges
• AC and DC Power Options

For full information visit the Field Mount Process Transmitters section of our web site (www.jhtechnology.com/field_mount.htm).
If you don't need a display, we also offer NEMA 4X and explosion-proof enclosures for our plug-in transmitter and alarm modules.

Our home page: 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/

Fast Response - Part 2

Speedy - Part 2

(See August 16 for Part 1)

Part 1 announced fast-response instruments. This time we're promoting our fast response to customer needs.

Thursday afternoon: We received two urgent calls, two different customers, asking "can you do it" and "how fast"? One was for 10 pieces of a standard product; the other, 6 specials which required modest new circuit design. We were able to say "Yes" to both.

Friday morning: Received both orders.

Friday evening: Two of us (Rick & Harry) stayed late.

Saturday: Rick & Harry worked from about 8:00 until 2:45PM. Finished both orders.

Monday: Both orders shipped. (Of course, both customers paid expediting charges to cover our overtime.)

Details: The standard-product order (JH4001I RTD Transmitters) was from a Navy base. They had been using "Brand A" products but that company was not able to delivery quickly. They sent searching and found us on the web. We did not have any in stock either - so we worked the weekend!

The special requirement was for an absolute-value transmitter. (See our posting of October 3, 2009 for more detail.) We had done this before (as a special in 2001) but the detailed requirements were different on this time. Thursday evening calculations plus weekend assembly and test got the job done.

Conclusion: If you need action, call us.

(800) 808-0300 or (941) 927-0300. e-mail jhtek@jhtechnology.com

Extended Temperature Operation

Too Hot? --- Too Cold?

Wouldn't you know - while this job was in progress we had another customer who needed to operate at high temperatures in a solar energy monitoring application. Same exact product (JH4380W), same exact solution. The extended temperature ICs support a temperature range of -40 to +85 degrees C (-40 to +185 degrees F).

We recently took an order (almost ready to ship as this is written) for 54 rangeable transmitters (JH4380W) to operate in environments as cold as minus 40 degrees (C or F - this is the one point on the temperature scale where both are the same). Our customer tells us the end destination is Russia. No great technological challenge - we simply built a run using extended-temperature ICs.

Link to our Specials & Customs page
Home page - all Process Transmitters & Alarms

Thermistors for Temperature Measurement

Thermistors for industrial temperature measurements? Sure - we just took a repeat order from an OEM customer (for instruments - we don't sell the thermistors themselves). So, I thought I'd write about them.

Let me identify myself - Harry Trietley, President & Chief Engineer. In the 1980s I worked at YSI (formerly Yellow Springs Instruments) who had once pioneered precision interchangeable thermistors. (They no longer make them - sold the product line off.) So, I had the opportunity to learn how to apply them. We now have two regular OEM customers.

You won't find thermistor info on our web site - maybe we should add it. For now, this blog is a start.

Thermistors are resistance thermometers but much different from RTDs (Resistance Temperature Detectors). RTDs are linear (approximately), wide range, relatively low sensitivity (about 0.4% per deg C) and increase with temperature. Thermistors are highly nonlinear, narrow range, high sensitivity and decrease with temperature (about 4% per deg C).

There are many types of thermistors - small, large, highly accurate, loose accuracy, many shapes. This blog is about NTC (Negative Temperature Coefficient) thermistors. There also are PTC (Positive Temperature Coefficient) thermistors that act more like thermal switches - increasing resistance rapidly in just a few degrees near the switching point. PTCs are not used for linear temperature measurement.

Precision NTC thermistors excel in moderate temperature, narrow range applications. They are very sensitive, and some have tighter accuracy specs than RTDs. One of our customers uses them in heating/air conditioning control; the other, precision measurements related to integrated circuit manufacturing processes. They also see wide use in medical and laboratory temperature measurement.

We have made simple adaptations of our signal conditioners (temperature transmitters) for use with thermistors. So far we haven't published standard spec sheets, but they are very similar to our other instrument styles. (See http://www.jhtechnology.com/).

If you have an application let us know. Each application is different as there are many thermistor types. We would need to start by knowing your measurement temperature range - also the thermistor type if you have chosen one yet. If not, we can help you find the right one. Probably best to ask for Harry.

e-mail: jhtek@jhtechnology.com, US phone (941) 927-0300 or toll-free (800) 808-0300.

Hello, visitors

We've only just begun .... A brand-new blog.

JH Technology, Inc. is an electronics company - we manufacture instruments known as signal conditioners, used mostly in industrial measurement and control applications. What is a signal conditioner? It's an amplifier for measurement signals. Signal conditioners amplify and convert signals such as temperature measurement (thermocouples, resistance thermometers and thermistors), pressure, force and weight (strain gauges, load cells), position (potentiometers), speed and RPM (tachometer pulses) and others. We don't make the sensors themselves, but we amplify and convert their signals.

We're a small, engineering-driven company and have strong capabilities in specials and custom or OEM products. We're also a bit old-fashioned - we answer the phone instead of running you around in circles with voice mail. We're proud of our customer service. If you need application assistance, have odd requirements or just need fast delivery, give us a try!

More "blogging" to come. Meanwhile, if you're interested, please visit us at http://www.jhtechnology.com/. To learn more about our specials and customs capabilities, visit www.jhtechnology.com/customs.

Of course, feel free to call:

Toll-free in the US (800) 808-0300
(941) 927-0300.