Setting up SCXI-1520/1314 for 1/4 and full brg. How short is a "short" cable length when jumpering terminals

[OKors]

As mentioned, I'm configuring my 1520 and 1314 for 1/4 and full bridge. In the 1520 manual it says: "for greatest calibration accuracy, use separate wires between the bridge and the SCA terminals. Do not directly connect S+ or P– to the
SCA terminals inside the SCXI-1314 terminal block unless the strain-gauge cable length is very short."

But then in the 1/4 bridge wiring drawing it tells you must directly connect the shunt calibration wires internally at the terminal block. 

So, how short is too short? The cables we use are typically 10-25'

[Broken_Arrow]

As for the differences in 1/4 and full shunt wiring.... 

• On the 1/4 bridge, when the shunt is applied, you are shorting out the internal dummy resistor (inside the 1314), i.e, the thing you are shorting is RIGHT THERE anyway; whereas...
• One the full bridge, when the shunt is applied, you are shorting out one of the legs of the bridge on the actual sensor, which may be far away.

As for how long is too long: Think of it this way: If you don't care about the extra resistance in the leads coming from your sensor while applying shunt calibration, then short S+ and P- internally and forget about it. If you DO care, then send the wires out to the sensor.

At 10', I would not expect any problems. Then again, I also didn't expect problems from not servicing the fuel filter on my motorcycle and it left me stranded in the woods in Alabama and now I cry myself to sleep every night.

Message Edited by Broken Arrow on 09-04-2009 07:40 AM

[OKors]

I'd cry too if I got stranded in the woods in Alabama! Did you hear banjos playing off in the distance?

Thanks for the input on the cable length. I'll have to look at our cable drawings, right now we've got an intermediate cable coming out of the 1314 (about 1' long) we connect all our 'house cables' to this.