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4-20 mA Converters

4-20 mA Converters

4-20 mA Converters

(OP)
Does anyone knows a single chip with the following characteristics:

Input: 4-20 mA as input from a field pressure/temperature
       transmiter.

Output: 0.1-2.8 Vdc (0-5 Vdc)as input to ADC.

I knew a couple of option but they don´t satisfy me. One is using galvanic isolators that have this characteristics (weidmuller/Phoenix Contact) but they are too expensive.
The other is using an AD620+some resistor..to weak.

Thanks.

RE: 4-20 mA Converters

Would it be easier to use a pressure transducer that did not include a 4-20ma converter?  That way you'd build an amplifier to accept the transducers mV output and amplify it to your needs.  Should be more accurate rather than converting from an already converted signal.

RE: 4-20 mA Converters

To Huff:

Using 4..20 mA signal is a very good means to transmit a signal reliable over extended distance in industrial installations. So ner68 should continue to follow the approach he has choosen, unless the transmitter is really close (<1m) to the electronics.

RE: 4-20 mA Converters

Burr Brown makes some but think you will find these expensive as well. Might be better off making your own circuit.

RE: 4-20 mA Converters

(OP)
Thank you all, I guess I´ll go for AD620 approach, and give it some robustness.

As for pressure transducer We use some conventional from Fisher-Roasemount, so I bounded to them.

RE: 4-20 mA Converters

I've used some signal conditioners from Pribusin ( http://www.pribusin.com ) and I've been pleased. They are not a single chip, though. If you have to go the single chip route, then roll your own with an op amp circuit.

RE: 4-20 mA Converters

To Electricuwe,

4-20ma has been used for longer distance purposes as you noted but from what I have seen it is a fading technology for such purpose.  A good 6 wire ratio-metric amplifier can easily be used with cables of 10-40'.  Some of our own signal conditioner boards are used with 100-200' cables with very good results.  Our boards are 24 bit with <.25uV noise being typical.  The trend lately though is to convert to a digital signal for transmitting long distances.  Each time you run a signal through another converter you induce one more source of error.  We do use 4-20ma for lower accuracy purposes when long cable lengths are needed but overall accuracy or resolution is not.

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