Petros Posted March 20, 2012 Report Share Posted March 20, 2012 Has anybody ever tried to use the PLC to make a power analyser / meter? It must be fun! Do you have a source for good CT's and PT's? Quote Link to comment Share on other sites More sharing options...
Walkerok Posted March 20, 2012 Report Share Posted March 20, 2012 I am unsure how well this will really work in the PLC since the scan times may (may not) create issues on your ability to catch peak data that you need. Now I have used the PLCs as simple panel meters without the power factor and efficiency calculations and that works just fine as you expect it would. The Unitronics does not give us a way to read amperage directly off of a CT since the raw values from a CT are generally ???:5 which means that on the side you want to measure it could be between 0-5 amps. So you are relegated to another level of isolation and need a CT with either a 4-20ma or 0-10Vdc output signal degrading the accuracy of your information just a bit. The lowest cost 4-20ma CT I have gotten from Dwer Instruments (about $30). If you have the ability to buy from Setra as an OEM they have a decent product for reasonable money. PTs are harder than Cts to get into the PLC. No one makes a PT with a signal the PLC can just pick up (generally 120VAC is what you have on the other side of a PT) You will have to make a dedicated circuit to convert the signal from AC to DC and reduce the voltage (but not degrade the accuracy) to a 0-10V signal. Keith Quote Link to comment Share on other sites More sharing options...
Petros Posted March 21, 2012 Author Report Share Posted March 21, 2012 I am unsure how well this will really work in the PLC since the scan times may (may not) create issues on your ability to catch peak data that you need. Now I have used the PLCs as simple panel meters without the power factor and efficiency calculations and that works just fine as you expect it would. The Unitronics does not give us a way to read amperage directly off of a CT since the raw values from a CT are generally ???:5 which means that on the side you want to measure it could be between 0-5 amps. So you are relegated to another level of isolation and need a CT with either a 4-20ma or 0-10Vdc output signal degrading the accuracy of your information just a bit. The lowest cost 4-20ma CT I have gotten from Dwer Instruments (about $30). If you have the ability to buy from Setra as an OEM they have a decent product for reasonable money. PTs are harder than Cts to get into the PLC. No one makes a PT with a signal the PLC can just pick up (generally 120VAC is what you have on the other side of a PT) You will have to make a dedicated circuit to convert the signal from AC to DC and reduce the voltage (but not degrade the accuracy) to a 0-10V signal. Keith Dear Keith, Thank you for your answer. These are exactly the issues I was worried about. Thus I also posted a request to Unitronics people to have a dedicated module considered that will enable such applications. Petros Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.