Loop calibrators

[flamy78]

Can somebody here explain the commercial use for loop calibrators? You know all the little devices that measure or output 4-20 mA DC usually at .1% +1 count or better and also read 0-100% .

I dont know if the AF is seeing these or not but Fluke makes the 787 and 789 and Altek, Transmation, and other companies make various models. I get the feeling they are used for motors or manufacturing or some kind of transducer. If you know anything I'm curious. There seems to be a nich market just for these. Oh also Omega.

I put this under k1/k8 because it is DC current.

   

[Aaron]

Although I haven't seen any loop calibrators as of yet, the Fluke 787 is for field checking process controllers such as the Honeywell UDC 3300 by producing a simulated input from an external monitoring device, and also verify the current output of the external monitoring device. These external monitoring transducers come in a wide variety of applications, temp, humidity, pressure...I calibrate several Mensor 4060 pressure transducers that are used in conjunction with these particular Honeywells. The 4060 can come in several pressure v current configurations, but the ones I cal produce a current anywhere from 4-20mA that corresponds to an applied pressure in a remote pressure chamber where they are mounted. This current output is applied to the controller where it is translated and displayed as an actual pressure reading. The 4060 also has RS232 capability and is cal'd using a PC to adjust the current v pressure output as monitored by a 3458 and a standard resistor, and adjusting the true pressure readings as monitored by the PC.

[howiesatwork]

As Aaron said they find use in process control, for the most part.
The advantage is that the sending and receiving parts of the process do not have to be in close proximity.
When using mV or V sensors with a precess, the lead resistance must be taken into account.

In a 4-20 mA loop system, lead resistance has no effect (unless your trying to push the mA through an extremely large resistance), so remote sensors are much more accurate in a wide-spread system.

We used to do a calibration of an HVAC system in a pharmaceutical manufacturing site that had feeds from three stories into the interstital floor between floors 2 and 3.  There were some 150+ pressure transducers, running from ±0.5"H2O to 0-15 PSI, along with the 100+ temp transducers.  Once we had the routine down, we could do it all in one and a half days with three techs.

Howie