Circuit Review

s1buell over 7 years ago

I`m currently making some proto circuits and I would love some feed back/Ideas etc.

All these circuits will connect to Arduino or Arduino compatible devices.

Anyone have time to help out with some reviews?

First circuit is a 4-20ma board

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genebren over 7 years ago in reply to s1buell +4

You might need to modify your 4-20ma loop front end somewhat. First, the circuit as shown does not have a return path for the current loops. Also, the current loop may not necessarily be directly referenced…
genebren over 7 years ago in reply to s1buell +4

Tom, Again, I am not sure that you can count on the second leg of the 4-20ma loop to be at ground potential. You might end up shorting out a driver or introducing ground noise into the circuit. Here is…
genebren over 7 years ago in reply to s1buell +4

Tom, Here is an even better link. This shows how to differential sense the loop current. https://www.sensorsmag.com/components/implementing-a-4-ma-to-20-ma-sensor-interface Good luck! Gene

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s1buell over 7 years ago

Wow missed that one. Completing the loop would be nice....
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genebren over 7 years ago in reply to s1buell

Tom,

Here is an even better link. This shows how to differential sense the loop current.

https://www.sensorsmag.com/components/implementing-a-4-ma-to-20-ma-sensor-interface

Good luck!
Gene
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genebren over 7 years ago in reply to s1buell

Tom,

Here is an even better link. This shows how to differential sense the loop current.

https://www.sensorsmag.com/components/implementing-a-4-ma-to-20-ma-sensor-interface

Good luck!
Gene
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abrain over 7 years ago in reply to genebren

Another useful source I found was instrumentation amplifier data sheets - the AMP04 from Analog Devices has a suggested 4-20mA receiver circuit that also shows some TVS protection diodes being used to protect the inputs, which could be useful in an industrial application?

A
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s1buell over 7 years ago in reply to genebren

Great info but I have a problem with the shunt resistors. My goal is to create something general to be used with most 4-20ma sensors.
Is this possible?

I checked out the AMP04 like the circuit but the -15 +15VDC supply becomes an issue.

I also found the RCV402 but there are expensive (old chip too). Anyone know of something newer and similar?

I though making a general 4-20 industrial loop would be easy…… well. Simple concept….. so many options….. lol

We sometimes use the Libelium 4-20ma device to connect to theses Siemens sensors. For sure the libelium board is not the complex.
https://www.google.com/search?q=libelium+4-20&client=firefox-b-ab&source=lnms&tbm=isch&sa=X&ved=0ahUKEwigmbOI2sHbAhVDlJAKHRdBCLQQ_AUICigB&biw=1093&bih=482#imgrc=cbzOIBxvMb2TTM:

Sensor:
https://w3.siemens.com/mcms/sensor-systems/en/process-instrumentation/level-measurement-with-level-measuring-instruments/continuous/ultrasonic/transducers/pages/echomax-xps.aspx

Control unit
https://w3.siemens.com/mcms/sensor-systems/en/process-instrumentation/level-measurement-with-level-measuring-instruments/continuous/ultrasonic/controllers/Pages/MultiRanger-100-200.aspx
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genebren over 7 years ago in reply to s1buell

Tom,

In the article https://www.element14.com/community/external-link.jspa?url=https%3A%2F%2Fwww.sensorsmag.com%2Fcomponents%2Fimplementing-… , the circuit only uses a general purpose op-amp to perform the differential reading and the single ended power rail should work nicely with Arduino. The shunt resistors are not that bad, it is just a matter of choosing as low a value as possible to get the voltage range you would like. Going too high on the shunt resistor runs a risk of existing the drive or compliance voltage on the xmitter side (10K @ 20ma = 200V, which is most likely greater that the drive voltage, 5-28V).

Looking at the Libelium devices, they are using jumpers on the receiver to manage the possibility that the xmitter is un-powered, so you could likely do the same. I have used any thing from 100Ω to 200Ω (2 to 4V max across the resistor).

Any generalize design will have a lot of variables when you are working with such an open protocol as 4-20mA loops.
Good luck!
Gene
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