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Fieldpoint with relays


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Hello

I've been having a difficult time with a bank of 8 fieldpoint modules controlling some ovens and valves. The modules would not respond to commands and Max would claim that the modules did not exist. Sometimes it would work fine and at the next power-on all is wrong again, even teh ready light did not come on in the modules.

To correct this I used two power suppllies, one to the Network module, and another to the supplementary supply that is connected from one module to the next. So far this is a big improvement...it works properly.

Can it be that the electrical noise is screwing things up.

Or is it the power requirements (I have 3 FP-RLY-420's in among 8 modules.)

Quote from the datasheet.

"Power Requirements

Because the FP-RLY-42x are high power consumption modules, they

could limit the number of I/O modules that you can connect to a

single network interface module. Controllers and network interface

modules supply up to 9 W to power I/O modules. The FP-RLY-420

requires up to 2.5 W"

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QUOTE (jbrohan @ May 6 2008, 10:02 AM)

Hello

I've been having a difficult time with a bank of 8 fieldpoint modules controlling some ovens and valves. The modules would not respond to commands and Max would claim that the modules did not exist. Sometimes it would work fine and at the next power-on all is wrong again, even teh ready light did not come on in the modules.

To correct this I used two power suppllies, one to the Network module, and another to the supplementary supply that is connected from one module to the next. So far this is a big improvement...it works properly.

Can it be that the electrical noise is screwing things up.

Or is it the power requirements (I have 3 FP-RLY-420's in among 8 modules.)

Quote from the datasheet.

"Power Requirements

Because the FP-RLY-42x are high power consumption modules, they

could limit the number of I/O modules that you can connect to a

single network interface module. Controllers and network interface

modules supply up to 9 W to power I/O modules. The FP-RLY-420

requires up to 2.5 W"

In my case I put all of the relay modules at the end of the string (away from the network module).

i also suggest you check with NI about the RLY-420's. Something tells me there was a recall for some FP widget. It may have been the RLY-420's.

Ben

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John,

Make sure that the inrush current on the ovens is within the max current spec of the relays.

In a similar FP application in the past, (hydrogen fueling station for fuel cell power plant) I had used the relay module to switch power to a second external relay with much higher current rating. Also add a diode to this second relay's input coil to avoid back emf problems.

Neville.

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