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Old April 20th, 2017, 03:55 PM   #1
boneless
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Galvanic Isolator

Hi all!

I will spare you the details as to why I ask this, but I am looking for a galvanic isolator that will limit its output to 4..20mA even tho the input may be 3.2..21.6mA. Any suggestions?

Thanks
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Old April 20th, 2017, 05:40 PM   #2
ASF
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A MicroLogix 1100 with a couple of GRT...MOV instructions would do the trick

I do have to ask why...this reminds me a lot of this thread from a few weeks ago...
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Old April 21st, 2017, 07:34 AM   #3
Stephen Luft
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Greetings,

Based on your description, I am not 100% certain this is what you are looking for, but will provide you with the information so you can further decide.

http://www.westermo.com/web/web_en_i...257893003E69DC

This product is currently in its end of life cycle, so I would need to check further as to its availability. So, please review the information and let me know if this will do what you are needing.

If you require additional information such as pricing, please let me know in that ESI is an authorized Westermo distributor.

You can also email me through the link provided below.
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Old April 21st, 2017, 08:46 AM   #4
osmanmom
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IMO mostly module generate output 4-20 ma ,base on configuration min and max setup
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Old April 21st, 2017, 08:59 AM   #5
boneless
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Thanks all!

Reason I ask is because we have a process that can run in two modes. In one mode, one of our transmitters sends out a failure signal (21.6mA) because the process is out of the measurement range. In our PLC we just deal with it, but the client who piggy-backs on the signal through a galvanic isolator cannot. For future projects we will indeed use an analog output instead, but this claim comes from a vessel, that could be anywhere in the world right now. So I am trying to resolve this "remotely".
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Old April 25th, 2017, 06:09 PM   #6
ASF
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Fair call. If it were me, I'd spend half an hour googling, and if I still came up blank, I'd just grab an analog click, put two rungs of code in it, and send it off to them with a wiring diagram. Hopefully you can find a neater solution, but it'd get you out of trouble if you needed it!
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Old April 25th, 2017, 08:20 PM   #7
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Quote:
Originally Posted by ASF View Post
Fair call. If it were me, I'd spend half an hour googling, and if I still came up blank, I'd just grab an analog click, put two rungs of code in it, and send it off to them with a wiring diagram. Hopefully you can find a neater solution, but it'd get you out of trouble if you needed it!
Been there, done that. Two rungs too. Mine was voltage, but the principle is the same. Note: All analog Clicks are currently on backorder. Expected May 17-19.
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Old April 25th, 2017, 08:59 PM   #8
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This is standard stuff. What your looking for is a programmable signal converter, also called signal conditioner.

They are normally isolated and you can program any input range to any output range and often you can program if you want to use voltage or current. In this case current input to current output.

As I said it's a standard automation component. You'll find them everywhere in the process industry.
They're used for a number of reasons. One is to provide isolation, another is to use as a calibration device to turn for instance a range of 5.4-17.2mA into 4-20mA, pure signal conversion like going from 0-20mA output to a 4-20mA output. They're also used to convert between voltage and current, for instance 0-10V into 4-20mA and vice versa. Some have programmable filtering of the signal as well. The really slim one are just 1/4" wide but you can larger modules as well, even some with displays if you want.

There are also many other types that does for instance PT100 to 4-20mA, frequency to current, analog to field bus etc so make sure you get the right type.

Last edited by Pete.S.; April 25th, 2017 at 09:32 PM.
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Old April 26th, 2017, 02:38 AM   #9
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Didn't post this before because it doesn't do the lower limit level and it isn't an isolator, apart from that it is exactly what you were looking for :

http://www.synectic.co.uk/sy042-4-20...p-limiter.html

You have to be careful using a click or any of the smart relays because of their limited A/D and D/A capabilities. The Click seems to be 12 bit which gives 4095 steps, which should be OK, but an Eaton Easy would only have 1023 steps which might be a problem.
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Old April 26th, 2017, 03:48 AM   #10
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I may have misread, but normally the sensors allow the user to define what to do in the event of failure (going to 3.6 or 21.6 mA or nothing). Is that a possibility for you?
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