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4-20 mA applications by FlukePlus members

May 2013

Verifying tank levels
Our facility uses many digital pressure transmitter cells (Rosemount) to measure levels in various tanks. The product in the tank puts force on the face of the cell, which sends a milli-amp signal back to the PLC (more level in tank = more pressure on face = more current sent). To test the accuracy of the levels, it's sometimes necessary to disconnect the wires to put a digital meter in series to measure the current. But, when we installed a new operating system, the PLC can detect a broken wire if we disconnect the DP cell and put the system into fault. Now with this new clamp on we won't have this problem any more!!
Shane Horn

Reading control cards
We are using a 4-20 mA output from our H2S and LEL Detcon sensors as input to our modular controller card. Most of the time we have a problem with getting a signal reading to the control card & its troublesome to break the signal line & connect the probes just to measure the mA signal.
Emily Sernio

Oil and gas production
I use my Fluke 87 and 787 daily and some times the ScopeMeter. Most of my applications are in oil and gas exploration and production offshore in the Gulf of Mexico. There are times when I have to shut in production to measure the 4 -20 mA loop of a transmitter in a hazardous area. The new clamp on 4- 20 mA meter would be a life saver for me.
Steve Johnson

Petrochemical uptime
I work on both process and environmental monitoring analyzers. This in some applications uses 4-20 loops to relay data to data recorders or to distributive controls systems. The accuracy and uptime of this equipment is very critical to process control and environmental compliance. I use a Fluke 705 and 87 in my field service work in support of the petrochemical industry. I have used Fluke Test equipment for 27 years and have found no equal in performance and reliability.
David Ellis

Loops as long as a football field
I work at one of this region's most state of the art water treatment plants where we run literally hundreds of analog instruments and loops 24 hours a day, 7 days a week. Because of the high reliability and ease of troubleshooting 4-20mA current loops we've come to demand it as a standard feature on all our instruments. We run current loops as short as a few feet and as long as two football fields in order to get a critical analog signal from its source to the nearest controller. In the process we have experienced many phenomena ranging from compromised wiring to static impulses from nearby electrical storms. Today we use a variety of loop isolators and converters to solve these problems so that we can keep our current loops running strong and reliable. One particular problem I've found involves today's variety of compact switching power supplies for industrial controls. Many colleagues have struggled with loops that experience roll-off at the top end of the range but without a clear explanation. Troubleshooting sometimes finds the loop's compact power supply can no longer supply full voltage at 20mA due to a newly added load on the loop or a failure of the supply itself hence, the output sometimes levels off at some point below 20mA while the loop voltage begins to drop. I use Fluke DMMs and DPCs to support all my loops and appreciate all the support Fluke engineers have given me over the years.
Gary Richardson

Rescaling PLC analog output
I just recently replaced a Japanese water valve actuator that operated on a 0-20mA analog output from a Mitsubishi PLC. The replacement valve was a 4-20mA device. I used my Fluke 789 Process meter to rescale the PLC analog output from 0-20mA to 4-20mA using the built-in controls on the analog card. My 789 gets dragged all over our plant. It's been a great tool for me.
Michael Mathews

582 loops and counting
The 771 Clamp Meter would be awesome for us! We use 4-20 mA loops all over our property for: - flow sensing (15+ loops) - HVAC controls (500+ loops) - temperature sensors (25+ loops) - pressure sensors (25+ loops) - differential pressure (10+ loops) - VFD controls (7 drives) - numerous other loops. The 771 would be an ideal troubleshooting and calibration tool for us.
Tony Fyffe

4-20 mA clarification
I just wanted to clarify why 4 mA is used instead of zero current. The main reason to use it is to improve the signal to noise ratio at low signal levels. The difference between 4mA and 0 mA is admittedly useful, not only in troubleshooting, but also to set a failsafe level when a current loop has failed and you need to send an alarm or default to a preset value.
Jay Henderson

Water flow monitoring
I am an shift electrician at a large steel company. With the energy sources of liquid steel, water is a necessity. Therefore, water flow and temps are continuously monitored by Rosemont flow and temp meters which feed 4-20 m\A back to a PLC and then read on remote HMI (Human Machine Interface). This 771 meter would be invaluable in determining if we have a water flow issue or a bad meter quickly. Much faster than having to unwire it to read the 4-20 mA output with some other Fluke DMM.
Jerry Evans

Promoting bacterial growth
I installed an ABB drive that controls two motors in a private sewage treatment facility. The 4-20 mA control circuit is monitoring the oxygen content in the aerator section of the plant and either speeds up or slows down the motor to provide the correct amount of air to promote bacterial growth. I only use Fluke tools for all my installation, trouble shooting and testing applications. In this case, I used my 87-111 DMM to set up the signal. Currently, I am running a Fluke 143 to monitor temperature in a nearby building to prevent freeze-up in our present severely cold conditions. I look forward to using your newest testing tools.
Mathew R. Magee

Reducing equipment failure
Using a standard Fluke 87 multimeter, I always used the mA point to check the actual value of our pressure transmitter, temperature signal, position transmitter and also current converter. Even though our transmitters are capable of HART and Field bus communication, we still use the reliable analog signal 4-20 mA. In our plant we have several hundred transmitters that need to use a 4-20 mA signal. On that new Fluke 771 clamp meter we will reduce the potential of equipment failure due to shorting the lead wire of transmitter or damaged fuse. It look like a more convenient measurement of 4-20 mA signal.
Joseph Jurado