Sharing Analog Signals

I'm using a Control Logix Chassis and i'm trying to share an analog 4-20 with a bently nevada. The card i'm using is an IF8. Is there a clean way of doing this without thinking too much out of the box? The bently sources the loop but not sure how to share the same signal between the PLC and the Bently. Any ideas?

Either a signal isolator or a signal splitter would work.

Take the 4-20mA loop through a 250ohm precision resistor, connect the ends of the resistor across the VinX+ and V/IinX- terminals(differential input) on the IF8 (where X=channel number) and configure the module so that 1-5V = 0-100%

You can convert the signal to 2-10VDC with a 500 ohm resistor across the 4-20mA leads. Once it has been converted to voltage, you can connect the signal to multiple analog inputs. The only caveat is that the inputs must be high impedence, because the impedence of those inputs will act in parallel with the 500 ohm resistor, and will slightly effect the reading. The higher the impedence, the less the effect. If you can measure the impedence of the connections beforehand, you can raise the value of the resistor to compensate, so the end result is 500 ohms.

This is not the cleanest way, but it is done everyday and works fine in most applications.

joboman said:

I'm using a Control Logix Chassis and i'm trying to share an analog 4-20 with a bently nevada. The card i'm using is an IF8. Is there a clean way of doing this without thinking too much out of the box? The bently sources the loop but not sure how to share the same signal between the PLC and the Bently. Any ideas?

Click to expand...

To ansewer your question, yes, but don't. Oakley has the best solution ( islolate) below is just one vendor, there are many others.

http://www.miinet.com/products/sg_signal.shtml

Many of the Bentley Nevada monitors have a re-transmission signal which will pass the vibration level to the PLC. I'd suggest you contact Bentley about this option. At the same time, you can ask them the question abut sharing signals.

If this is a new installation you might also ask about availability of vibration monitoring modules that drop right into the A-B PLC rack. They have that available for some systems. Note that Bentley has a broad range of transducers, transmitters, and monitoring equipment. Don't automatically assume the transmitter is giving you a 4-20 mA signal.