pressure transmitter low insulation

[jalover]

Hi! is there anybody who can tell me why the pressure trnasmitter connected to our ups 24 vdc showing low insulation alarm in in the UPS panel. ups is supplying 24vdc to signal acquisition unit (plc) if we disconnect all the sensors (pressure trnasmitter- p/I converter) alarm is gone but if we connect these sensors alarm coming in the ups panel which is low insulation. pls advise what are the possible remedy on this. i'm thinking that the electronics circuit made it becoming low insulation when connected to ups battery, example capacitor inside the trnasmitter circuit. is that possible? any thoughts on how to solve this problem? thanks a lot in advance. more power to all of us.

jalover

 

[danw2]

What brand and model of power supply are you using to power the transmitters? It is a different power supply than powers the PLC processor? The UPS is not the 24Vdc power supply, correct?

Which brand/model UPS is this? I'd like to read what the manufacturer means by 'low insulation'.

What brand and model pressure transmitters?

Does the alarm occur when only one pressure transmitter is connected, or do multiple pressure transmitter need to be connected to trip the alarm?

 

[jalover]

hi Danw2. thanks for your reply. the ups unit uses an an output of 24vdc from battery bank, 400vac input supply used for charging unit. this 24 vdc is powering the whole plc unit and all the trnasmitters are connected to plc input for monitoring purposes. ups is customized made by saiernico in china , trnasnmitter is also china made. even with only one trnasmitter connected . it always trigger the alarm, any one of the trnasmitter when connected will trigger the alarm. the ups has a panel board consisting of charging circuit, voltage reg, voltmeter, ammeter and low insulation monitoring unit. this ups supplying the whole signalling acquisition unit but finds me very strange why if any of the transmmitters connected it gives an alarm. hope you can give me more techinical advice.

 

[roydm]

Your 24 VDC is likely grounded at some point, I suspect at the PLC (on purpose).
When the transmitter is connected the UPS sees the 4-20 mA signal through transmitter-through PLC input to negative (ground) as a fault.
Check the PLC input negative, i am sure you will find it there.
You can probably lift the ground and allow system to float at UPS negative.
Roy

 

[danw2]

Try Roy's suggestion. I suspect that 'low insulation' might mean ground fault (low resistance leakage path to ground) indicated by a current flow, an indicating ground fault circuit.

Out of curiosity, are these pressure transmitters the only input devices to this PLC or are there other input devices?

I noticed that Saiernico is a marine ship builder. I am clueless about ship power systems.

Is it common to run 24Vdc as ship power? Is it convention to ground one side of shipboard DC as a common, like the negative ground on 12V automotive systems?

Could the battery bank be grounded as a common?

Dan

 

[jalover]

Hi Roy,

Thank you for the prompt reply and input. I will look into this further.

 

[jalover]

Hi Dan,

thanks a lot for your continous input. There's still a lot more input devices ( digital & analog) but only these 5 sensors giving an earth fault indication. disconnecting these 5 sensors will give healthy condition. I suspect these chinese made trnasmitter giving fault indication, i just wonder why happened for all. ship's power utilizing 24 vdc coming from battery bank and this is connected to a float type charging circuit, other way is by using rectifier system ( 220vac to 24 vdc) , but in our case we're using battery bank but not grounded as a common.