So what I need to ensure proper scaling with the Eurotherm Drive is what PLC output i am using?
Yes, first you need a copy of the Eurotherm DC Drive User Manual. I searched and found Eurotherm User Manuals here (Models ER-340i / ER-680i / ER-1220i in DC drive product manual HG102938):
http://www.eurotherm.co.uk/download...13385=6401&search=Motor+Drive&searchcontent=1
but not the "Series 529". That may be an old no-longer-produced model, or it may have another model number. It appears that the Eurotherm DC Motor Drives do have a 0-to-10 Volt DC voltage potentiometer input for the Motor Speed Reference Input. There are two ways to input the speed setpoint: on drive terminals 2 (0 volts DC) and 3 (10 Volts DC maxium); or on a Ramp Input (terminal numbers for Ramp Speed Input varies with model of Eurotherm DC Drive). For the normal Terminal 2-3 Speed Input, you would use the PLC to control the Ramp Time as in my previous program. For the Ramp Speed Input, you set the ramp time with internal drive programmable parameters, then input the max speed that the ramp stops at.
I am not using any additonal cards etc. Just the MicroLogix and its inputs and outputs that came on the processor.
I do not think you would have any analog outputs available with "what came on the processor". The best I know, the MicroLogix 1500 has slots for add-on modules, and I think you will need an analog output module to allow sending a scaled speed signal to the Eurotherm DC Drive. To know what your MicroLogix 1500 has, look for the original PLC model number, which then can be looked up on the Allen Bradley site at
http://www.rockwellautomation.com/products/
I suggest downloading a copy of the MicroLogix 1500 User Manual, Bulletin 1764. This manual shows that the 1500 normally is solde with only digital outputs, so you will not have an analog output unless you add an Analog Output Expansion Module. That is now your most important task, to determine HOW to get the speed signal to the Eurotherm.
Now, on many VFD AC Drives, there are digital terminal inputs that allow sending preset digital (on/off) speed control signals, but the best I can determine, the Eurotherm DC Drvies DO NOT have any preset speed input terminals. You need to verify that by getting a copy of the manual for the Eurotherm drives that you have.
Do I need to scale the RPM to the output of the drive to motor, plc to drive, or what?
Yes, you will need to do scaling. If you do manage to procure a MircoLogix 1500 Analog Ouput module, then you would use that to send your scaled speed signal to the Eurotherm drive. I think you would need to use the 0-to-10 VDC range, so if you use the Engineering Units setting for the MicroLogix 1769-OF2 Analog Output module, you would scale your speed output (O:4.0 in my last sample program, 0 to 39 RPM) to the digital count range of 0 to 10000. I can give you the scaling equations for that, if needed. You would just add two more rungs (one for each time your send a number to your DC Drive) to the end of the program and use the SCP(Scale with Parameters) instruction, which is available on the MicroLogix 1500 PLC. For the SCP instruction, and for a RPM range of 0-39 RPM, your SCP parameters would be:
Input: use a suitable memory location instead of the existing Output O:4.0 (N7:0 to N7:255 can be used here).
Input Min: "0"
Input Max: "39"
Scaled Min: "0" (This is a digital number that will produce a 0 VDC output at the analog output terminal).
Scaled Max: "10000" (This is a digital number that will produce a 10 VDC output at the analog output terminal).
Output: O:4.0 (the location of your 1769-OF2 Analog Output. If you do not use Slot 4 for your analog output module (Slot 1 will be the first expansion module slot), then change the address to the actual slot used by replacing the "4" in the O:4.0 address. The "4" is the module channel output number, 0 being the first analog output number).
With the above parameters, the SCP instruction will take your Ramp numbers and pass then to the Eurotherm DC Drive speed input terminals. For example, if your send "39" to the input of your SCP instruction, then the Output will be computed to be "10000" (or 10 volts).
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).
