convert 0-10v to 4-20ma

Have a question.
Have a transducer that gives a 0-10v output. Is there a way to add a resistor so that it would appear as a 4-20ma signal?

E=i*r

If you start with something above 0, it is mathematically impossible to get down to zero.

You should be able to add a resistor and then do something with your scaling, if your input card only accepts 4-20mA

how would you add the resistor, and what value.

After more thinking, umm.. no. I would recommend an E/I transducer.

irondesk40 said:

Have a question.
Have a transducer that gives a 0-10v output. Is there a way to add a resistor so that it would appear as a 4-20ma signal?

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I don't know of any way other than retransmission with something such as this

A 500 ohm resistor will get you there. I don't know that you'll need true 0 though. Ohm's law gives you the answer. ex. 10V by .020 mA. I used this method a time ago for controlled water valves.

phish13 said:

A 500 ohm resistor will get you there.

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Well it will give 0-20mA

But if irondesk40 can change 0-10V to 2-10V. Then is the 500 ohm

lbg_dk said:

Well it will give 0-20mA

But if irondesk40 can change 0-10V to 2-10V. Then is the 500 ohm

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OHMs Law

0-10V with a 500 will not work,

its other way around 4-20 with a 500 ohm gets you 2 - 10VDC.
A 4 - 20 ma output is driven by a contsant current generator. It will mantain 4 -20 ma regardless of the circuits total impedance, up to a point. That is why there is a limit on how many devices can be hooked up in series with 4 - 20 ma

With the voltage output the 500 ohm is in series with whatever the impedence of the circuit is.

irondesk40 said:

Have a question.
Have a transducer that gives a 0-10v output. Is there a way to add a resistor so that it would appear as a 4-20ma signal?

Click to expand...

A good chance not. But that all depends on what the input device actually is. Some devices are really voltage input only measuring with exernal resistors or dip switched. Others are internal and don't mess with it or have a very low impedence (some recorders are 50 ohms). Remove the resistor and you may have a 0-10v input, but it has a good chance of being 0-5v. If that is the case you would use a voltage divider to only look at the 0-5 volt portion. The device then needs to be scaled properly. If you aren't sure what I am saying, or this isn't the case, then go with some kind of converter. See 'curlyandshemp' post or any of the many manufacturers of these devices. It pays to have some laying around just in case. There isn't much worse than you are gone and a new guy has to work on it an sees this glob of stuff hanging on the input terminals. Of course we are all great on our documentation so that would not be a problem .
Tell us what kind of devices you are using? There may be a chance that the 0-10v output may not drive a low impedence load. I believe most voltage inputs are relativly high impedence and your transducer assumes that. So too low of a load will give you problems.

You need a "signal conditioner"--basically a high-volts range transmitter similar to what would be used for a TC.

You can't do what you want to do using conventional resistor array and have a 4/20ma range.

See Omega's TX1506-2 as an example of one of these devices.

Sorry I was thinking in reverse and when I did use the resistor method it was to get the voltage input from the current input. I shouldn't be posting when I'm half asleep.

Most voltage outputs have a minimum resistance in the load of several k Ohm. Putting a resistor in the circuit won't work. You can get a signal conditioner from AutomationDirect for $119. You can't do a lot of engineering and testing for that amount of money.

What i ended up doing was ordering a phoenix contact converter to convert the 0-10v out of a linear transducer to 4-20ma.

The original designer had installed a new control system, but for some reason had chosen to not change the linear transducer. At that time he installed a series of resistors that must have worked good enough to get the system running, but technician changed out the linear transducer last week with a new transducer, and it no longer worked. So, instead of trying to fight through it, just ordered the phoenix

curlyandshemp said:

OHMs Law

0-10V with a 500 will not work

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LOL I am sorry to tell you but it do work.

Do you want me to make you a drawing ?

But as Tom Jenkins mentions first check the output impedance first.

irondesk40 said:

So, instead of trying to fight through it, just ordered the phoenix

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At my work we have programmable converter on stock. Some times you don't want to fight customer / fabricator / manager