Frequency Converter (VFD?) signals from PLC

Greetings Experts!

We are planning to use a couple of frequency-convertes (or is VFD the correct English term?) to adjust the speed of some pumps.

These are relative small motors (1,5kW). We have not decided for witch manufacturer of VFD we are going to use, but it will probably be telemecanique.

My question is, from a PLC I/O point of view, what signals are needed to control the VFD?

My guess is that it must have a analog output value (4-20mA) for speed reference, and a digital output run-signal. And also a digital input signal for run-feedback? Is this correct?

Regards
JSMtek

JSMTek said:

Greetings Experts!

We are planning to use a couple of frequency-convertes (or is VFD the correct English term?) to adjust the speed of some pumps.

These are relative small motors (1,5kW). We have not decided for witch manufacturer of VFD we are going to use, but it will probably be telemecanique.

My question is, from a PLC I/O point of view, what signals are needed to control the VFD?

My guess is that it must have a analog output value (4-20mA) for speed reference, and a digital output run-signal. And also a digital input signal for run-feedback? Is this correct?

Regards
JSMtek

Click to expand...

Typically, that's those are all of the basic signals that you will want. You may want to monitor a second digital input (Drive Faulted), and/or an analog input (speed feedback).

Vfd

If controlling with I/O, everyone has his own way of wiring.

Maybe you want to control the drive with the keypad on the drive... maybe you want a start_button, with a speed setpoint (potentiometer) and and 2 outputs, one for running signal and one for alarm. Maybe you can add a reset button, ... there is not really a standard I think.

Frequency converter is correct. Some people say inverter, this is not really correct, inverter is the part between the motor and the DC-link. The inverter is the part in a converter that modulates the frequency to the motor, for regulating.

JSMTek said:

Greetings Experts!

We are planning to use a couple of frequency-convertes (or is VFD the correct English term?) to adjust the speed of some pumps.

These are relative small motors (1,5kW). We have not decided for witch manufacturer of VFD we are going to use, but it will probably be telemecanique.

My question is, from a PLC I/O point of view, what signals are needed to control the VFD?

My guess is that it must have a analog output value (4-20mA) for speed reference, and a digital output run-signal. And also a digital input signal for run-feedback? Is this correct?

Regards
JSMtek

Click to expand...

yes good enough
some drives can talk with plc over network maybe this is an option.
Are the pumps able to run lower speed? some fans can not.

Personally I use an analogue PLC output (1-10V) to control speed, and a digital output to run/enable the drive (via interposing relay). From the drive I monitor the drive fault relay which is present on most VFDs

I have also used 485 multidrop with a small number of drives on some applications to better monitor/control the drives (reading the current/frequency etc to the HMI).

Rev

My first preference would be to select a PLC with built-in analogue outputs.
[Example http://www.omron247.com/doc/pdfcatal.nsf/9483DBE1DAFBD4C08625742400622D1B/$FILE/CP1H_PLC_Datasheet_P06E.pdf].

Analogue add-on expansion modules always seem to be a premium price from most PLC manufacturers, so if you do not have them on the base CPU I would suggest one of the following:-

Select a drive that accepts a digital pulse train input for speed reference and drive it from a high speed output of the PLC.

Use a PWM output of the PLC and a simple resistor/capacitor circuit connected to the analogue input of the drive.
[See link http://www.plctalk.net/qanda/showthread.php?t=35572].

These are the conventional I/O's

Digital inputs

a)Start

b)Fault ( From VSD fault relay)

c)High Discharge Pressure

d)Low level ( in suction manifold or in tank from which pump is sucking media)


Digital Outputs

a) RUN command for VSD

b) Alarm beacon

Analog inputs

Pressure signal ( 4-20 ma or 0-10vdc)

Analog outputs

4-20 ma or 0-10 volts output to VSd for controlling speed

Hope this helps

Cheers