1746-ni8

[Splash 0]

Trying to build a robotic torso using potentiometers as control and feedback. I built the Control panel a SLC 5/03 with 1746-NI8 cards and was trying out some pots to see if i was on track, when i go online the values for the analog inputs only go from 9988 to like 10276. I got a 10VDC power supply feeding my pot and the wiper and other pin going the (+) input on the card and the card (com) going back to the power supply. What could my problem be, only thing i havent done yet was ground the (-) side of the power supply or the PLC chassis, go this be my problem? any other suggestions? Edited 7 Mar 2006 by Splash

[Ken Moore 23]

Whats the resistance of your POT? The NI8 is looking for a 4-20mA signal. As we know, I = V/R .020 A = 10volts / 500 ohms .004 A = 10volts / 2500 ohms So the range of your POT needs to be somewhere around the above. Try to get just one channel working and then expand from there.

[jstolaruk 9]

Sounds like you've wired it like a current input but need it setup for a voltage input. Couple of items: change the voltage/current select switches to voltage. One leg of the pot should go to your power supply, the other leg to the common of the power supply and common of the input card. the wiper should go to the analog input. I'd put a couple of small resistors inline with the two legs of the pots and the wiper to the analog input. That will keep the wiper from ever actually touching ground and power and eliminate any excess bias currents to the analog input (in case the it could happen) and wiper contact. User Manual is here: http://search2.rockwellautomation.com/texi...id%3D43a61cc72e

[Splash 0]

The module is set for voltage input, and i'm using a 10K pot with a 10VDC power supply

[jstolaruk 9]

have you enabled the input in your software?

[Splash 0]

The input is enabled when i hook up the pot it goes to full scale when i unhook it goes to zero, but when i use the pot to adjust the voltage it doesnt really do anything. I think from you previous post i probally have the pot wired wrong, i'm gonna try that.

[panic mode 246]

make sure to connect ends of pot to 10V source. negative end and pot wiper will go to analog card input configured for voltage. you probably didn't connect one end of the pot to the negative side of 10V supply so you always get full scale because input card has much bigger impedance than your pot.

[David Nelson 3]

you may try putting a resistor across the pot itself. some pots used for heavier loads back in the days of antiques would need a very slight load on them to see an actual voltage drop from the wiper. but use caution and start with a very high resistance

[Splash 0]

OK i got it fixed, wired it like jstolaruk said and it work like a charm. Thanks for yalls help.