Generate 0 - 10 VDC using Micrologix 1400 Series B

Greetings Experts,

I have a project where i am supposed to apply load to an element. Now the value at which load is to be applied is known and i am reading it from my load indicator through RS-485 Modbus RTU protocol. The load application starts when i give 0 - 10 VDC to my servo drive. The speed of the load application depends upon the voltage applied to my drive. When 10 VDC the load is applied quickly and at 0 the drive stops which means that load is not being applied.

I want to generate 0 -10 VDC in my plc when i write current load value and set point load value to the plc's memory. Thus plc should generate the voltage value accordingly using PID algorithm. That generated VDC will control my drive speed. If i apply the voltage in -10 - 0 VDC then drive is running in reverse direction which means the load is being released.

Can i full my requirement of controlling the drive using PLC. I can write the current value and set point value in my plc's memory.

Any help would be grateful. I don't know much about hardware.

Yes
What type of servo is this
Are you aware of the analogue control setup. You said -10 to 0 to + 10 is that correct

You are going to use Modbus. Why not also control the servo

What type of element load are you controlling.
Does this require torque limitation/control

Thanks for the reply.

Its Panasonic Minas A5 and 1.5Kw. I am not from the hardware side all i know is how MODBUS works. The servo vendor told me to apply voltage between -10 to 10, which means if voltage is from -10 to 0 the motor will run in reverse direction and stops at 0 Volts. If voltage is from 0 - 10 it will run in forward direction.

The servo motor is attached to ball screw. The load will be applied to my element when servo runs in forward direction i.e. if applied voltage is from 0 - 10. At 10 volts it runs at full speed in forward direction. To release the load negative voltage is applied from -10 to 0. At -10 volts the motor will run in reverse direction full speed. To stop the motor 0 volt is generated and the motor stops.

Now generation of -10 to 10 volts is important. This can be done using PID algorithm (that's what i know). We can also go for on-off approach but it's not recommended. I have the setpoint value and process value which i can feed to any device that can generate the voltage necessary to drive the servo. What i know is that in Micrologix 1400 Series B there is PID function which i can directly use, but i don't know whether i can generate the desired voltage range i.e. -10 to 10 volts.

Now generation of -10 to 10 volts is important. This can be done using PID algorithm (that's what i know).

Click to expand...

Uh, not exactly. The PID only generates a numerical value that is PROPORTIONAL to a 10 volt output (0 = 0 volts, 16383 = 10 volts). To get the actual voltage you need some type of digital-to-analog converter. Usually that is a Analog Output Module that takes the numerical Control Variable from the PID (0 to 16383) and converts it to the equivalent voltage output. For the Micrologix 1400, I think it has a couple of built-in analog outputs. If so, then you must add a logic rung to take the PID output and scale it and send it to the address of one of the MicroLogix 1400 analog voltage outputs.

Check the specifications in your ML 1400 User Manual to see what analog outputs are available and what are the voltage ranges. If you do not have the manual, you can download it free from this link:

http://ab.rockwellautomation.com/Programmable-Controllers/MicroLogix-1400#/tab5

Yes, the ML 1400 has 2 analog outputs, but the voltage range is only 0 to 10 volts, not -10 to +10 volts. However, when the PID output goes to < 0, you could use a comparison statement to check the digital value and use that to send a digital signal to your servo to change direction.

Another possibility is that you could use BOTH analog outputs, with one wired in reverse to the servo to give the 0 to -10 volts. Your PID signal would have to be split and scaled to produce the two different voltage ranges. For instructions on the ML 1400 PID instruction, see the MicroLogix 1400 Reference Manual, Chapter 20, page 291.

If you have an AB analog output module it appears you could only generate 0-10 VDC not -10 to +10 VDC.
Spectrum Controls has a unit : 1762sc-OF8
http://www.spectrumcontrols.com/pdfs/abio/1762sc_OF8_datasheet.pdf
that will do the bipolar thing for you.
If you don't have an analog output card at all, I don't know of a way to do what you need.

Thanks a lot guys. Sorry for late reply.