Electronic Potentiometer

[Deke 0]

I want to automate the speed control on a Blowmolding machine that has a DC drive (Reliance MaxPak Plus Controller), based on input from the machine I know the machine is ready for the next cycle, but this is dependent on the speed of the extruder for filling plastic into the head. I want to be able to progammably change the speed based on how many seconds it waited or was to fast. Currently we have a 5K 4-turn pot controlling the speed. I was thinking of using a Electronic Potentiometer along with a Unitronics PLC, just wondering if anyone has done something like this and have knowledge that may help me on this project. I have the logic done! But I was wondering about the Electronic Potentiometer, as to what brand and size? Found some made by Megacon, has anyone used these? Thanks Deke Edited 22 Dec 2004 by Deke

[Crossbow 294]

Personally I'd replace the pot with an analog output from the PLC. If you're going to have to write logic in the PLC to control the process, you may as well give it direct control over the speed of the drive.

[Deke 0]

Hi Chris, Thanks for replying. Now I thought about doing that first, but found this problem; The Unitronics PLC requires that the common from the analog signal be the same as the one supplying power to the PLC(24V), so that took that idea out. I did find some isolated analog in/out modules made by Dwyer that look like they will work for this and the part numbers are MSP-V-IN & MSP-V-OUT. The source from the Drive's Controller is 12V, the max power limit going to the pot has already been adjusted via the controls on the Drive control and is at 8.3V, which is then adjusted by the operator pot for speed control. That is where I want to suppliment the controls by adding an electronic potentiometer, which would only be active during the machine's Auto cycle, when in manual the pot would still be the controlling the drive speed. Is this correct that I need an isolated analog? Thanks Deke

[Deke 0]

Thought I'd let you know, that I did order the MSP-V-OUT, as per there Tech suport, I will be able to use the analog out on the unitronics (using it set at 4-20mA) plc to the MSP-V-OUT module. Also found out that Dwyer dosen't really make them, Sensorpulse does and I found all the files at their website for downloading. So when I get this all together if anyone is interested, I'll update this thread with the results, good or bad. Thanks, Deke

[panic mode 246]

Baumer makes MDRM18U9524 and you will also need magnet 123344. sensor has voltage output and working range of 160deg (not 4 full turns). scroll down for MDRM This is as close to electronic potentiometer as I can think of but you can always use small encoder... signal isolators are qute common and there are plenty of companies making them (Weidmuller, Phoenix Contact, ... ).

[Deke 0]

Well it took a little while to work out the the exact settings but it works like a charm! Ended up using an Micrologix 1000 with Digital Out as there were drivers already made up for this plc, that along with 4 Relays from AC devices I energize the relays which gives 24v DC to the Micrologix Inputs, runs through the logic and automatically adjust the drive controller's speed using the MSP-CV-OUT module, when the machine is not in auto (manual) the pot still controls the speed. Now there's no more excuses as to why the machine is running slow, operators can't slow it down, as the pot only works in manual, the plc keeps the speed within one second from cycle to cycle, much more consistent. less wear and tear. Boss says you can put this on each machine now! :) Deke