First Program

SOMETHING TO CHECK: Find out what RPM your motors are actually running. If these are DC gearmotors, then most likely the motor is running much faster than the motor gear-reduced output speed. The PLC probably needs to use the actual motor speed range (not the geared output range). The only exception would be if the DC Drives are programmed to take the gear-reduction ratio into account on their speed input range. You can compute the actual motor speed range if you find the gear-reduction ratio (assuming that these are gearmotors).

Question for you again: How is the speed of the drives controlled right now, before your PLC ramp progtram is installed?

Cassandra,

Yes, we can give you detailed information. First, how much do you know now? Where do you want to start?

Andrew, going back to basics again, the only clue you have give about what method is used to control the 5 DC Drives was from your boss here:

He wants me to now just use timers to accomplish this. Meaning I don't know the exact calculation, but after I hit the pushbutton it will take say 5 secs to reach the first desired RPM of say 15 RPM's. Again thats not exact. He then said after you reach that RPM, use another timer to start the 60 sec cycle at that RPM.

Click to expand...

The above could mean that your DC drives have some preset speed ranges, and your boss wants you to use timers to set each step speed for TT seconds.

Like I have said before, you are doing this project backwards.

1. First, determine what equipment you have, what the capabilities are for each device.
2. Find manauals, instructions, wiring diagrams for all equipment.
3. Now write the PLC program.

You started with Step 3, so naturally you will have a lot of extra problems, and will be doing your program over when you find out what inputs the DC Drives can accept.

Some motor drives have communications capabilities (Devicenet, Ethernet, and so on) and many PLCs also have those capabilities. Where there is a direct communications link between the drive and the PLC, it is possible to set the drive speed without a PLC analog output module.