Monitoring starter motor amps

Kmrunner · Mar 31, 2009

Bear with me, I'm new to the PLC world. I want to use an existing SLC-505 with Ethernet connection to monitor the amps from 8 300hp screw compressors with AB starter motors. I'm trying to find the simplest way to monitor the 3-phase amps and get that info into the PLC so I can monitor and change the PLC program that turns our compressors off and on based on system air pressure. If I can monitor the amps, I have an Excel spreadsheet ready so show the realtime capacity readings of the compressors that can be viewed from any PC with access.

PLC's and motor starters are AB. I have a DeviceNet module available and various analog and digital input and output cards. I can buy other items if I can just figure out what to get.

Can anyone offer some suggestions? I haven't had much luck from the local vendors figuring this out.

bkottaras · Mar 31, 2009

Kmrunner said:
Bear with me, I'm new to the PLC world. I want to use an existing SLC-505 with Ethernet connection to monitor the amps from 8 300hp screw compressors with AB starter motors. I'm trying to find the simplest way to monitor the 3-phase amps and get that info into the PLC so I can monitor and change the PLC program that turns our compressors off and on based on system air pressure. If I can monitor the amps, I have an Excel spreadsheet ready so show the realtime capacity readings of the compressors that can be viewed from any PC with access.

PLC's and motor starters are AB. I have a DeviceNet module available and various analog and digital input and output cards. I can buy other items if I can just figure out what to get.

Can anyone offer some suggestions? I haven't had much luck from the local vendors figuring this out.

If you have VFDs instead of simple motor starters you could add a Device Net Interface option to each VFD and get a whole lot of info for each one of then via Device net.
If you do have motor starters only, current transformers on each phase of each VFD could do the trick.
You already have the Device Net Scanner, option modules for the motor VFDs aren't that expensive.
On the toher hand, current transformers on each phase of each motor and such as well as the analog Input modules and the labor will add up to the bill quickly.

plc noob · Mar 31, 2009

This is another option http://literature.rockwellautomation.com/idc/groups/literature/documents/pp/193-pp017_-en-p.pdf

Roy Matson · Mar 31, 2009

Greystone make a nice converter either clip on or wire through.
You only need to measure one phase because it should be balanced.
The converter is a two wire device with 4-20 mA output

Roy

http://www.greystoneenergy.com/English/products/power/products_power_sensors.html

Mickey · Mar 31, 2009

Here's another option:

http://www.loadcontrols.com/products/products.html

JSPLC · Mar 31, 2009

If you go with the VFD's like bkottaras suggested you should be aware of the electrical noise these units gererate and how that might cause some problems with other systems connected to those mains.

Kmrunner · Mar 31, 2009

Thanks

Thanks for the links. LoadControls has a nice power cell but might be too pricey. I'll check on it. I found some Power Monitors and Power Transducers from http://www.nktechnologies.com/products.html

that might do the job if I assume a balanced load. For what I'm doing that should be a good assumption. It looks like I can wire these directly into an analog input card.

I want to watch what capacities the compressors are running at during the day since they're such a big electricity user in our plant. We have 8 300hp compressors and 5 200hp. If you don't run them near 100% you waste a lot of money.

milldrone · Mar 31, 2009

Kmrunner said:
I want to watch what capacities the compressors are running at during the day since they're such a big electricity user in our plant. We have 8 300hp compressors and 5 200hp. If you don't run them near 100% you waste a lot of money.

Kmrunner,

Welcome to the forum!

So you are looking to save some money, and you have singled out the air compressors as the prime target. Compressed air in most industrial environments is a very expensive commodity. If you have not already done an air energy audit. Put the audit on the top of your list of things to do.

An audit is not just about fixing leaks. I have personally witnessed the end result of an audit increasing production and lowering air consumption at the same time.

zankorel · Mar 31, 2009

Kmrunner said:
Bear with me, I'm new to the PLC world. I want to use an existing SLC-505 with Ethernet connection to monitor the amps from 8 300hp screw compressors with AB starter motors. I'm trying to find the simplest way to monitor the 3-phase amps and get that info into the PLC so I can monitor and change the PLC program that turns our compressors off and on based on system air pressure. If I can monitor the amps, I have an Excel spreadsheet ready so show the realtime capacity readings of the compressors that can be viewed from any PC with access.

PLC's and motor starters are AB. I have a DeviceNet module available and various analog and digital input and output cards. I can buy other items if I can just figure out what to get.

Can anyone offer some suggestions? I haven't had much luck from the local vendors figuring this out.

What manufacturer and model are the compressors? If they are Atlas Copco, then they can supply units which give diagnostic information over ethernet on the units. I assume other suppliers have equivalent monitoring gear.

Alternatively, you could put in some smart overload protection relays on the compressors which would give you amps, assuming you also installed some CT's. Allen Bradley ones would probably be the go, since you have an SLC5/05 already

Monitoring starter motor amps

Kmrunner

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bkottaras

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plc noob

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Roy Matson

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Mickey

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JSPLC

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Kmrunner

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milldrone

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zankorel

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