Ge Fanuc Plc

Wish i could help you with specifics but,

I have just purchased a 5 DVD disc set, A Guide to Understanding PLCs @ http://PLCS.net

Regards,

Jim

What is the analog input set up for and where is your signal coming from? AI cards for the 90-30 are either 0-5VDC, 0-10VDC or 4-20ma. 2.6mV is way too low for the average PLC analog input to see, let alone respond to accurately. You will need to amplify it using what is called a "signal converter".

If that 2.6mV is from a thermocouple (TC), you either need a converter that is made specifically for that TC type, i.e. J, K, N, T etc. and convert it to 4-20ma, or you will need to buy a specific TC analog input card. Unfortunately for the 90-30, the TC input cards only come in 4, 6 or 8 channel versions, so they may end up being a lot more expensive than just finding a converter if you already have a 4-20ma AI card.

thanx for the replies

I kinda suspicioned the low voltage would be a problem and that an amplifier would be needed. Thanks a lot for verifieing that for me.

I'm thinkin my best bet would be to go with an electronic temp sensor that would read off the thermocouple. And if I ever get all this damned snow removing done, that's what I'll do.

I'd suggest you purchase a specialised temperature controller instead. RKC is one brand, there are many others. They don't cost much and will simplify everything.

Wire the T/C to the controller and it'll have a built in display, adjustable setpoints, adjustment for various sensor types, broken lead detection and a voltage free output to tell the motor to go.

Another thing you could do is simply use a thermistor-based temperature sensor. You'd want to wire the series circuit like this: Ground, series resistor, temperature sensor, 5V supply. Measure the resistance across the series resistor. If you use an NTC (negative temperature coefficient) sensor like this one:

http://www.rs-autosport.net/catalog/product_info.php?cPath=10&products_id=215

the voltage across the series resistor will go up with temperature. You'll want to choose a resistor with a value that is approximately what the resistance of your temperature sensor will be in the middle of the range of temperatures you'll be measuring, in order to maximize linearity of your voltage measurement. The voltage output by this setup will work very well with your analog input. The resistance vs. temperature curve for this sensor can be found here:

http://www.megamanual.com/v22manual/mwire.htm#clt

(scroll down a bit until you find the table.)

You can set up an Excel spreadsheet to calculate a series resistor voltage vs. temperature curve very easily.

The added benefit of using a sensor like this is that it has 3/8" NPT pipe threads, so you can plumb it right into a tee fitting in your water plumbing, if that's where you want to measure the temperature.

Hope this helps,

-Rodney

Are you using Proficy ME or LogicMaster90 software?