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4-20ma help

4-20ma help

4-20ma help

(OP)
I'm looking to drive a toy train from the analog 4-20 of a slc 500.. So I'm not sure on how to convert 4-20 to 0-12vdc with a 1A load capability. Is there a product out there that will do this? I use I/P at work all the time, but I can't find an I/E in any of our catelogs that will drive that much load. I also thought about using a 0-5VDC card to drive the base of a power NPN transister with 12VDC feeding the collector. If I use the Emitter of the transistor to drive the load will I get a linear drove from 12 to 0 or will it act like an on off switch?

RE: 4-20ma help

You could use a time-proportioned routine with a fairly high switching frequency to drive a discrete output (0-5 V) that turns a solid-state relay on and off to supply voltage to the train. The duty cycle of the output will then determine the voltage applied to the toy train.

xnuke
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RE: 4-20ma help

Check out Absolute precision instruments, they have many converter options.

RE: 4-20ma help

Driving your current loop over a calibrated resistor gives you voltage. If you apply that voltage to an op amp which drives an NPN driver, with it's output feeding back to the opamp, you'll have a very simple yet effective driver, that is linear.

RE: 4-20ma help

(OP)
Thanks for the info guys. Automatic, do you have a generic schematic? should I use a 4-20ma at 24vdc source or a 0-5DC source? I just need to figure out the easiest way to get 12VDC with a 1AMP max draw..

RE: 4-20ma help

Look at:
http://hmin.tripod.com/als/andysm/pages/analogs6.html
Scroll down to the bottom of the page, and pick out a
suitable circuit.  Sub your derived voltage for the
feedback circuit in the diagram.
There are simpler ways, but I do not have handy examples.
<als>

 

RE: 4-20ma help

There are lots of hobbiest (like this post) pre-built voltage regulator circuits that you can just buy. I have posted links before so I'm sure if you spent some time searching my previous posts you'll find something. There were a few sties selling ready to use circuits for exactly what you want. Also, Google is your friend if you search for the right terms.
 

RE: 4-20ma help

I rememberd what I searched for last time - "PWM DC motor controller".

You'll have to change the PLC to use 0-20mA so the train will stop.

Feed a 12VDC power supply to the circuit.
Feed 0-20mA into a 600ohm resistor and it is converted to 0-12VDC.
Your output will be 0-12VDC capable of 6.5A.

http://store.qkits.com/moreinfo.cfm/K8004

 

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