4-20 ma conversion

Shaun · Dec 16, 2002

I have an application where,
1. I am using a 4-20ma pressure transducer signal.
2. I need to turn different lights on at off at different pressures.
3. At this time I don't have access to the existing old PLC system, so I am seeing if there is such a device that can do this conversion for me,

any ideas?

Tom Jenkins · Dec 16, 2002

In all probability you can do what you want, as long as the PLC has an analog input. You would simply use compares to see if the pressure is greater than a set value for each light, and if so turn on an output wired to the light in question.

Shaun · Dec 16, 2002

thanks Tom,

but I am trying to do it without a PLC.

john paley · Dec 16, 2002

You need a threshold switch. We have some built in to some of our old analog drive systems and use some stand alone models to enable / disable different things based on tach feedback voltages. The thing basically looks at the analog value and switches relays in/out at different, adjustable levels. Ours plug in to a standard 11 pin round pin relay socket. We got them froma place called Action Instruments. They make all kinds of neat gizmos for analog levels.

Shaun · Dec 16, 2002

thanks John,

it looks like you are right.
Quote is coming as we speak.

cheers

rsdoran · Dec 16, 2002

I am not sure what the process is but there are also controllers dedicated to this type application. Honeywell is one manufacturer:
http://www.lesman.com/unleashd/catalog/control/control_udc6300.html

Cost wise if all you have to do is turn on/off a few lights at X ma then a low cost plc may be the best fit.

Tom Jenkins · Dec 16, 2002

Look at Omega Egineerings controllers. They are made for PID control, but several models also have multiple alarm outputs. Anotehr option is limit alarms from M-Systems, Entrelec, Phoenix, A-Pi, many others.

jvdcande · Dec 17, 2002

Try a LM3914 IC and a resistor. The LM3914 is a circuit which converts a voltage to a LED bar (or is it the LM3915?). You need the resistor to convert from mA to V. This is the simplest and cheapest solution possible.

Kind regards,

Jean Pierre Vandecandelaere

oorozco0 · Dec 17, 2002

shawn

I think you can used a programmable indicator that has several output alarms contacts which you can program at different pressure pts.

Hope this will help you!

shooter · Jan 5, 2003

use a VU meter circuit
or a battery check circuit.

4-20 ma conversion

Shaun

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