Current Flow Monitor

Hello All! First post time .

I am looking for a device which will connect to my RTU/PLC Digital Output Board. The device functions as follows:

1. A digital output signal is generated by the RTU
2. The device checks all the relays in the field to check if any of them are active.
3. If a relay in the field is active the device will reject the Digital Output command.

I have read some documents on this device and apparently it is known as a Contact Weld Deteciton Module or Current Flow Monitoring Module. But I have not come across a device which fits this exact functionality.

Any help is appreciated. Thanks!

tstarks said:

Hello All! First post time .

I am looking for a device which will connect to my RTU/PLC Digital Output Board. The device functions as follows:

1. A digital output signal is generated by the RTU
2. The device checks all the relays in the field to check if any of them are active.
3. If a relay in the field is active the device will reject the Digital Output command.

I have read some documents on this device and apparently it is known as a Contact Weld Deteciton Module or Current Flow Monitoring Module. But I have not come across a device which fits this exact functionality.

Any help is appreciated. Thanks!

Click to expand...

Hi TSTARKS,

I've not come across such a module and google didn't have any pointers but that doesn't mean one doesn't exist!

I'm having trouble understanding your application and what you are trying to achive. can you help me out with the following:

Is the RTU/PLC responsible for switching all the relays in the field from digital outputs on the PLC or simply monitoring the status of them?

If the PLC is responsible for switching the relays, surely all you would have to do is monitor an axilliary contact off the relay and feed it back into the input card of an RTU/PLC. Then in the PLC code, if the auxilliary contact is made but you haven't set the output to enable it then the contact could be deemed welded from prior use.

Alternatively, electrically could you not wire the output in series with the required relays so if the relays contacts are in the wrong position the ciruit would be broken and hence the resulting output would not be true?

Are you trying to reduce the number of inputs you require to your RTU?

Cheers,

Lee

Look at safety relays http://www.mew.co.jp/ac/e_download/control/relay/power/catalog/mech_eng_sfw.pdf

http://www.sti.com/

You can use any current relay on the market. I use the model DIB01CB485A from Carlo Gavazzy. If the relay detects any current above a certain value, the contact closes, and you can wire it to the PLC input. Finder also as a similar relay.

That is not what he was asking for...at least I do not think it was.

He wanted a way to monitor relays..to be more precise, contactors/starters, in case they stuck in the ON position.

I think he can do it with this relay. If all the power going to all the starters coils, relays etc. passes through the current relay, then he knows by reading the adjusting the current on the current relay if atleast one starter is ON. This ralay can measure the current above 0.1Amp. I use this many times to detect if atleast one solenoid valve is open. If I have at least one valve open I> 0,35A, then I turn on the cold water pump. In his application is just the inverse.