Applying Excitation Load to the SCXI-1520

[dj143]

We use the SCXI-1520 signal conditioner to test and calibrate bridge sensors that we manufacture and it works great.  While the system is not used (i.e. when the operator connectes a sensor to the system) the SCXI-1520 is automatically isolated by using relays in a switching system.  The primary intent for this is to avoid possibly damaging the signal conditioner.  (Operators do regretful things.)   This means that the excitation power is floating with no load while the signal conditioner is disconnected,.  I was wondering if it would be appropriate to have the system automatically apply a load resistor to the excitation source to keep it "warmed up" so to speak.  Most sensors are a 350 ohm bridge and may be as high as 5000 ohms.  I was thinking of applying a common 330 ohm 1/2 watt resistor as a load.  (We are currently only using two channels at a time.)  Although I'm sure it would not make things worse, I just wonder if it's worth the bother.  Please advise...

[Logan_K]

In my opinion, I don't think it is worth the trouble. The temperature of the SCXI-1520 probably won't change much from connecting a load to the exictation since there is plenty of heat generated from the SCXI-1520 to keep it at a stable temperature with or without the excitation source being connected. A bigger concern would be that strain gages can have self-heating errors when current is applied, which is usually accounted for by using a Quarter Bridge Type II configuration with a dummy strain gage next to the active gage. These self-heating errors occur when the strain gage is connected to the excitation source - so if you wanted to keep anything "warmed up" it should actually be the strain gage that you are disconnecting; not the SCXI-1520.

-Logan K