6 channel signal Amp

[bob4]

Hi all, Im putting together some test gear and need to boost the signals from 6 inputs, pressure tranducers & Thermocouple. The inputs will give me 2-20mA but I need 2-10vDC.
If I could get a single module that's compact and runs on 12Vdc I'll be happy.

Any Ideas??

 

[ScottyUK]

2-20mA input? 4-20mA is very common. I've never seen 2-20mA before.Thermocouples are mV devices. They'll require a different type of signal conditioner to the devices with a mA output. Your biggest limitation in choice is likely to be the 12V DC power supply: is there any chance for you to use 24V? This is the standard industrial control voltage, and there is a vast choice of equipment available.

A few companies who make signal conditioners which I have used and been pleased with:

http://www.prelectronics.com

http://www.actionio.com/

http://www.status.co.uk/

There are literally hundreds of others to choose from. If you can provide a 24V supply (or AC mains) the

http://www.prelectronics.com/filer/5111uk.pdf

is a very configurable unit which would handle mA or mV inputs and provide the output range you need.

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I don't suffer from insanity. I enjoy it...

 

[danw2]

I, too, believe that your devices probably output 4-20ma, a worldwide industrial standard.

You don't need a module, you only need a resistor to get 2-10Vdc.

Ohms law shows that 4ma through a 500 ohm resistor drops 2.0Vdc.
20ma through a 500 ohm resistor drops 10.0Vdc.

So you need run the 4-20mA signal through a precision 500 ohm resistor and connect either side of the resistor to the input of the device looking for 2-10Vdc. Or, as the techs say, you wire the 500 ohm resistor across the input.

The devices that output 4-20mA are known as transmitters.

There are 4 wire transmitters that output a signal on two wires (+ & -) and use another 2 wires for power.

There are 2 wire transmitters (also called loop powered transmitters) which require that a DC power supply with sufficient voltage to drive the loop resistance be wired in series with the output signal.

Any 2 wire transmitter will have a graph or spec that tells how much resistance its output can drive. Your transmitters will have to be able to drive at least 500 ohms plus the resistance of your wiring with a specified voltage. I suspect 12vdc will not be enough for a 500 ohm load.

The spec sheet on my desk for a brand name pressure transmitter shows that 12Vdc will only drive about 100 ohms. It takes about 22Vdc to drive 500 ohms. Higher power supply voltages (within a spec typcially like 11-38Vdc) will work. The suggestion for using a standard 24Vdc power supply is appropriate.

Dan

 

[bob4]

Slip of the pen with 2mA, must learn how to use these things.
The project is based on a portable unit which will use it's own batery pack and recharge direct from a vehicle power supply.

OK, I could use a 24 cell and string a few voltage regulators off it but not realy what I was intending.


The spec is compact and light.

Bob

 

[danw2]

Laptop batteries approach 20Vdc nowadays.

Why would you "string voltage regulators off it" ? What does that accomplish?

Can the 2-10Vdc input be changed to 1-5Vdc (which would use a 250 ohm resistor) or a 0.5 - 2.5Vdc input (which would use a 125 ohm resistor) or some other lower range?

 

[powerjunx]

"Can the 2-10Vdc input be changed to 1-5Vdc (which would use a 250 ohm resistor) or a 0.5 - 2.5Vdc input (which would use a 125 ohm resistor) or some other lower range?"


Better use 250 ohm precision resistor.

 

[circuit1952]

A precision resistor is inexpensive, compact and requires no power supply to convert a 4-20mA signal into a 1-5V or 2-10V signal. If the signal is shared by different devices, you may have ground loops or other interference. In that case, a signal condioner such as ScottyUK mentioned may be necessary.