PLC Servo Control

John Marston · Feb 15, 2019

Hello All, I design a PLC system (multiple PLC platforms) to control a servo valve that positions a hydraulic cylinder. The setpoint is given to me by the customer, feedback is provided by cylinder mounted LVDT (or LDT), and the servo is driven by a +/-60mA signal.

My problem is, there's only one manufacturer that I have found that has a device that can provide an output of +/-60mA. From my PLC, I output a 4-20 mA CV signal to the converter which then converts the signal to +/-60mA that goes to the servo. The converter I use is a Axiomatic IC-DR-13. It works great but it isn't CSA/CE or rated for hazardous areas.

Would a typical servo amplifier work? I need something with a 4-20 input and a +/-60mA output.

James Mcquade · Feb 15, 2019

what is the hazardous material and rating?
you will need to establish this first.

Parker makes a control board also, you might check into them.

where is the servo and lvdt located?

if the cylinder is in the hazardous area,
use an intrinsic barrier for the lvdt.
the signal will then go to the controls and tell the servo what to do.
the servo would be n the non hazardous area if possible.

regards,
james

John Marston · Feb 15, 2019

Typically my plc/hpu/servo/cylinder will be in a class 1 div 2 area located in a refinery, so explosive atmosphere. I've looked at one Parker board (BD90/95) that was suggested by my distributor but I couldn't find much information about its certs either.

Peter Nachtwey · Feb 15, 2019

You don't want to use a BD90/95. That is ancient analog and pots technology from the late 1980s. I doubt it is Class 1 div 2 rated.
We sell a Class 1 Div 2 hydraulic servo motion controller but it doesn't output that much current by itself. We can add a VC2124 voltage to current transducer that will convert the +/- 10 volts to +/- 60ma but I don't know if that will meet the class 1 div 2 requirements.
I work for Delta Computer Systems, we make hydraulic motion controllers and the voltage to current converters. I suggest calling and asking to talk to David Shroyer. He is the one that did the class 1 and div 2 certification for us. He would also know about the valves and MDT rods or can at least find out. Our controller has been used in oil and gas applications before. The problem is getting the right combination of things that are all class 1 div 2 and work together.
www.deltamotion.com

James Mcquade · Feb 16, 2019

Can you put the controls in nema 7,9 enclosure and do the work?
these are the massive bulky enclosures 1/2" thick.

another solution is a nema 4/4x enclosure that is purged or pressurized.
you will have to do the risk assessment for either application.

regads,
james

John Marston · Feb 18, 2019

Peter Nachtwey said:
You don't want to use a BD90/95. That is ancient analog and pots technology from the late 1980s. I doubt it is Class 1 div 2 rated.
We sell a Class 1 Div 2 hydraulic servo motion controller but it doesn't output that much current by itself. We can add a VC2124 voltage to current transducer that will convert the +/- 10 volts to +/- 60ma but I don't know if that will meet the class 1 div 2 requirements.
I work for Delta Computer Systems, we make hydraulic motion controllers and the voltage to current converters. I suggest calling and asking to talk to David Shroyer. He is the one that did the class 1 and div 2 certification for us. He would also know about the valves and MDT rods or can at least find out. Our controller has been used in oil and gas applications before. The problem is getting the right combination of things that are all class 1 div 2 and work together.
www.deltamotion.com

I believe that my coworker called Delta last friday and we are looking at purchasing the VC2124. We have another servo that works with +/-10 V that we plan to use with the VC2124. I can't remember who he talked to but they asked him why we don't just use modulating valves, which is funny because that's what we want the hydraulic guys to switch to beforehand.

John Marston · Feb 18, 2019

James Mcquade said:
Can you put the controls in nema 7,9 enclosure and do the work?
these are the massive bulky enclosures 1/2" thick.

another solution is a nema 4/4x enclosure that is purged or pressurized.
you will have to do the risk assessment for either application.

regads,
james

We typically use purged enclosures and/or Nema 7 or 9 enclosures but the converter is the key. It isn't certified for CSA or CE and that gives a lot of trouble when going international.

PLC Servo Control

John Marston

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James Mcquade

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John Marston

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Peter Nachtwey

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James Mcquade

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John Marston

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John Marston

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