converting4-20ma to 0-10v

pls give me idea to convert 0-20ma to 0-10 volts.

U=R*I

The easist way I have found to convert from mA to VDC is to use a Action Pak. You just have to configure the dipswitches to get the desired result. They take up very little panel space and are quite reliable.

mj's answwer is the most reliable. In addition to Action Intruments you can get the signal conditioners from M-Systems, A-Pi, Acromag, Phoenix contact, and all kinds of alternate suppliers.

guest's answer is actually the one I use most often, but it's acceptability depends on the transmitter. If you use a 500 Ohm resistor in the loop you will get 0-10 VDC from 0-20 mA. However, transmitters have a maximum allowable load. For most this is in the area of 600 to 750 Ohms, but some are lower and most are a function of the loop power supply voltage. Check your transmitter specs and all other loads on the loop before you use that technique.

Tom

I haven't had the need to yet but is it possible to install the resistor and leave it there for future checks?
I know that will depend on the sensor and the amount of load, but will the reading be the same afterward installing resistor?

The reason I ask is the only place we use 4-20ma is in continuous operations that I can't disconnect the sensor (install meter or other device) without shuting a line down.

Thanks
Drewcrew6

I'm a little fuzzy on your circuit, Drew, but I think the answer is yes.

If the analog input on the PLC is voltage and you are running the loop current through a resistor to create a voltage drop, you can pull the PLC I/O module and the transmitter 4-20 mA will operate undisturbed.

If the analog input to the PLC is current, you can't put a resistor in the loop. The 500 Ohm external resistor would be in parallel with the 250 Ohm internal resistor on the analog input card. The net result is that 1/3 of your loop current would go through the external resistor and give erroneous readings.

Now, a trick I have used in the past is put a Zener diode, reverse biased, across the input wiring at the field terminal strip. You have to watch your voltage drops, of course, but if you use, let's say, a 12 volt Zener and a 250 Ohm impedence input, the zener won't conduct when the analog card (or any other loop device for that matter) is there. If you yank the card the Zener will conduct and the transmitter won't know the difference.

Okay that makes sense.

What I was looking for (which you answered) was if I install a resistor in the loop (series) then I can hook a meter up and read the 4-20ma signal as a 0-10v signal and verify my loop is working properly. And to adjust the signal from the transmitter without having to "break into" the loop.

There is a panelview readout but it is some distance away and not very easy to use when adjusting the sensor (adjust- walk over and check- re-adjust- walk over check- again and again).

I know it will take some time to get the relationship curve between the 2 types of signals but that aint no big thing.

Thanks
DREWCREW6

http://www.kele.com/olcat/default3.html
Sorry that only takes you to a search page. The transducer is
model UAT2

Now that I understand your objective, I have a couple of other suggestions.

1) If you know the impedence of the PLC (most are 250 Ohm) you can just measure the voltage across the input. 4-20 mA = 1-5 VDC. Watch out though - sometimes loop powered units on non-isolated inputs will give different readings.

2) I always use disconnect type terminal strips on 4-20 mA loops. These have a switch between the field and panel terminals. (AutomationDirect.Com has them as part number DN-KBD12 for example, but I usually use Entrelec.) Then you just put your meter's probes on each side of the terminal block, flip the switch open, and now your meter is in series with the loop without loosing continuity. After you get your reading flip the disconnect down and pull your probes.

Slick-Trick, Tom!

I've got a ton of those switches. I use them to isolate inputs/outputs or simulate inputs.

You might remember, with respect to transducer inputs, I have hot stand-bys that switch automatically or at my request. That allows me to do anything I want with the off-line transducer.

Your trick will make it so I can do more with less in those cases I need to. Cool!

BTW this thread would be easy to classify under "4-20mA".

Just one caution here. 4-20ma will not give you 0-10 or any other 0-anything volts. Across 500 ohms you will have 2-10V and across 250 ohms half that. My point is that you will have to either get the current loop to operate down to 0ma (many do) or build a low end offset voltage into your voltage input.

Another trick I've used to measure current in a loop without having to open circuit it is to install a diode in the loop, forward biased. It will conduct with approx 0.6 v drop. To measure the loop current connect your ammeter across the diode to short it out, the diode will not be conducting and the loop current will pass through the meter.

paulc20,

Likewise, Cool!

DAMN! Ain't 'lectrical things fun?!