Analog sensor connections

RayK · Jun 26, 2007

I'm confused! which is the correct way to connect an analog sensor? top circuit is from the AB1762-IF4 manual lower one from the Redlion manual.

RYoumans · Jun 26, 2007

The top one is the preferred way.

Mickey · Jun 26, 2007

RYoumans said:
The top one is the preferred way.

Why??

If the transmitters are current TX (i.e 4-20 ma) then they are both correct.
The current is the same in a series circuit.

RYoumans · Jun 26, 2007

Yes, a loop is a loop. It's just better practice to have power supplies feed the transmitter first, and then the measuring device. This is the way you'll see it wired most of the time.

Mickey · Jun 26, 2007

RYoumans said:
Yes, a loop is a loop. It's just better practice to have power supplies feed the transmitter first, and then the measuring device. This is the way you'll see it wired most of the time.

Ok. I too connect it like the top drawing, I like to fuse the "+" connections from the PS to the Transmitter. The TX is usually outside the cabinet and the PS and I/O module are inside. I like to protect against any thing going bad in the outside world.
But better practice? And thats the way you see it most of the time. Not so sure of that.( maybe)

panic mode · Jun 26, 2007

in case of 1762-IF4, inputs are isolated so both circuits will work. the thing is that not all analog cards are like that...

RayK · Jun 26, 2007

Thanks for that Guys, instincts said either but as its a Redlion sensor maybe i'll use the circuit in there manual. thanks again for the replies.

mellis · Jun 27, 2007

From the installation instruction for the 1762-IF4 (Not IF4I)

System Wiring Guidelines

Consider the following when wiring your system:

• All module commons (ANLG COM) are connected in the analog module.

The analog common (ANLG COM) is not connected to earth ground inside the module.

• Do not use the analog module’s NC terminals as connection points.

• Channels are not isolated from each other.

• Use Belden™ 8761, or equivalent, shielded wire.

• Under normal conditions, the drain wire and shield junction must be connected to earth ground via a panel or DIN rail mounting screw at the analog I/O module end. Keep the shield connection to ground as short as possible.

(1)

• To ensure optimum accuracy, limit overall cable impedance by keeping your cable as short as possible. Locate the I/O system as close to your sensors or actuators as your application will permit.

• If multiple power supplies are used with analog inputs, the power supply commons must be connected.

Bottom line, I think either way will work for one sensor. I think you will have problems wiring more than one sensor with the bottom arrangement.

RayK · Jun 27, 2007

multiple sensors?

So this arrangment is a bit sus?

Analog sensor connections

RayK

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