Numerous SCC-SG24 appear dead when used with strain gages

[Mark Reznicek]

I have four SCC-SG24 Full Bridge Strain Gage modules which I can install in (any) one analog socket of a SG-2345 system. I stick to the J1 socket to rule out it's influence. Two of these modules appear completely dead (both the X and X+8 bridge outputs), one appears to have low sensitivity, and one appears fine (both the X and X+8 bridge outputs). I've installed into each a pair of 30k resistors into R1 and R5 so that I can null the bridge using the trim pots.

I've picked one socket of the SG-2345 and individually connect each of the modules which I've attached to a load cell which contains a full bridge of strain gages. I use the test panel of the NI explorer to read the X or X+8 input to the module and relay in/out the cal resistor And one by one it appears that the X and X+8 input channels are dead on two of these modules except one which has both input channels working fine. I have three tests that I try (1) null the bridge by turning the trim pot, (2) connect the 301k SCC-SG11 shunt resistor to unbalance the bridge, and (3) apply force to the load cell to unbalance the bridge. I carry out these three tests on the X and X+8 channels of the module.

Test (1) Test (2) Test (3)
=======================================================================================================
Module1 X, X+8 ok X, X+8 ok X, X+8 ok
Module 2 X, X+8 no change X, X+8 no change X, X+8 no change
Module 3 X, X+8 no change X, X+8 no change X, X+8 no change
Module 4 X, X+8 no change X, X+8 no change X, X+8 small observable change but
not as much as for Module 1

Two of the dead modules are brand new and the other two had been fiddled around with as we were/are learning to use Labview and the SG-2345, etc.

I'm either destroying these modules or my setup is flawed. How do I trouble shoot my setup?

[LA 75]

Hello,

You may want to check the way you are configuring your SCC modules in MAX (when creating Tasks for instance.) I would like you to see two figures that I am attaching below please (although they are for thermocouple Tasks, the idea is the same in Strain Gauges): 1. Note that in the first attachement (Wrong Temp) the temperature is compleately off and constant (appears to be dead), this is due to a wrong physical channel configuration 2. In the second attachement (Right Temp) the temperaure now makes more sense, the physical channel is correct.

If this is the problem, then you need to make the correct selection from the physical channel options when creating a Task. Right click on DAQmx, select Create New, Analog Input, Strain. Then another window is going to appear where you can select the different supported physical channels available for you to use. Don't select a channel for you device (DAQ board), instead select a channel from your SCC module (i.e. SCC1Mod1)

Please let me know if this solved the problem.

Thanks!

LA

[LA 75]

...forgot the attachments

[Mark Reznicek]

Hi - Thanks for help. And you are right. I was incorrectly using the input for the DAQ card when, as you pointed out, I should be using the input from the SC connector block. I'm new to using this equipment and your advice will save me frustration in the future. It is weird, though, I made the change and still have my same problem. I am going to return the strain gage modules to NI for repair.

Mark

[LA 75]

Hello,

I'm glad my support was of help to you. Before you send your module for repair, I would advice you to check on the following (it can save you time and money):

1. Check that your connections are right.
2. Probe with an oscilloscope the voltage before it gets to the module and compare it to the voltage you are reading in the Test Panels of Measurement and Automation Explorer.
3. If you have other modules of the same type, try them out and see if you are getting the readings you are expecting. If you are getting the correct readings with these other modules, then probably the module in question needs to get repaired. If all of them are failing, then probably you are not configuring them correctly.

Hope this helps,

LA