4-20ma help 1

[noguru]

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?

 

[xnuke]

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
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Thedroid]

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

 

[automatic2]

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.

 

[noguru]

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..

 

[fsmyth]

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>

 

[LionelHutz]

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.

 

[LionelHutz]

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