Flow meter analog output question...

Matchu04

Lifetime Supporting Member
Join Date
Mar 2013
Location
Northampton
Posts
287
As my confidence grows with working with multiple control systems, I am starting to take more and more on, where before I would just pie it off. (I would like to say this is mainly due to the help from you guys on this site). I have managed to trip my self up a few times along the way in simular situations and hence require some guidence from you guys once again.

My Issue..

I recently had to verify a flow meter (a E&H 53p80 for those who are interested) and for for what ever reason it failed and had to replace it. My issue came when disconnecting the feed back loop cables. I was under the impression that as the unit had 24v to it, it would used this to power to loops. So removing this supply would isolate it. However when I disconnect them, after isolting the 24v supply, I soon realised that this wasnt the case and shorted them out against some main beer line and needless to say a 20 min job just got longer.

Is this my fault for assuming...? Are feedback loops normally fused inside the main panel to protect the PLC so should have isolated it there.

How would you guys go about it?
 
First off that appears to be a mag meter. These require quite a bit of power, so I am assuming that this is a four wire transmitter. It's possible that the 4-20 was loop powered or powered by the transmitter. You need to verify the entire circuit - I can't answer your question without more info.
 
The E&H meters (models I have worked with) have jumpers that allow you to set active/passive modes. So depending how someone typically designs the circuit these may or may not have to be changed, especially if you are replacing a meter. I had a similar problem, meter was replaced and no signal finally found the jumper reference in the manual.

I would hope you have a good set of prints? Reviewing the wiring at the IO card should aid in determining what is supplying power.
 
I aggree with the other posts. It all depends on how many wires are coming in. Usually Loop powered means you'll only have 2 wires but as Tom stated mag meters can have up to 4 wires. In this case you would have to find the circuit feeding the meter and isolate it. The analog circuits are usually always fused in the PLC/DCS panel.
 
It's hard to say which wires you were playing with. Depends on the exact model which defines what the output assignment is. Same with the power; manual says the supply voltage should match the nameplate supply. Could be DC or AC depending on model.

For integral meters with the converter/transmitter mounted on the flow tube, there are only power and output signals. But for remote mounted converter/transmitters, there are typically 6 additional wires in a cable from the converter/transmitter to the flow tube, coil and electrode excitation and signal wires.

< 1% of magmeters are 2 wire loop powered that have a DC power supply in the circuit. The E&H Promag 53 is NOT a 2 wire loop powered magmeter, it is 4 wire meter with separate power wires..

The vast majority (99%) of magmeter converter/transmitters are 4 wire instruments; 2 wires for power, 2 wires for the output signal.
 

Similar Topics

I have a Flow meter that returns a 4-20 signal and the problem I have is the pump is a diaphram pump so theres alot of pulsing causing my...
Replies
19
Views
7,990
I have a plc 5/40L I have the analog input coming in to the card at a raw count. I can get the flow but how do I total the pounds into a reg. Do I...
Replies
5
Views
4,399
Dear All, I need a sample PLC program to count the output pulse of a mass flow meter so that a specific amount of mass (for example 100gm)can be...
Replies
2
Views
82
Morning Guys, I am installing a turbine flow meter with a pulse output to measure flow on a compactlogix 5069 -L306ER through a 1734-VHSC24...
Replies
3
Views
1,555
I need modbus communication tool for Yokogawa Rotamass Flow meter? can any one help me.
Replies
1
Views
971
Back
Top Bottom