Differential Readings (two load cells)

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ed1
Differential Readings (two load cells)

I have AIN0_1 for load cell#1 and is working fine.

I connected AIN2_3 for load cell#2 with all settings checked same as load cell#1 but is not reading.  Checked and verified the connections and settings and is all good.  the load cell #2 works fine on AIN0_1.  I have DAC0 outputting 4.75v used by both load cells.  I also tested connection to AIN2_3 without any connection to AIN0_1 and still does not work either.  So, something about AIN2_3 is disabled; where do I start troubleshooting after having both connections and settings checked out?

LabJack Support
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If you excite a bridge

If you excite a bridge circuit with 4.75 volts, the signal voltages should both be about 2.375 volts at no load.  Use a DMM to measure AIN2 and AIN3 both versus GND and confirm this.  Also measure AIN2 to AIN3 to confirm it is close to 0 volts, and note the actual value as your no load offset.

Next add a known load and measure AIN2-AIN3 again to confirm it has changed as expected.  For example, if you have a 100 pound load cell specified for 2 mV/V output, it should give you 2*4.75 = 9.5 mV at 100 pounds.

 

ed1
I can only confirm there is

I can only confirm there is activity at the moment; on the other hand, I've attached a screenshot of LJControlPanel with nothing attached to the unit.  I'm wondering if this is indicating there is a problem with AIN2/4 pin; all the others noticeably fluctuates.  What do you think?

File Attachment: 
LabJack Support
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The LabJack is usually not

The LabJack is usually not the problem, so my first guess would be that the voltages on AIN2 & AIN4 versus GND are indeed 0.000033 volts.  My previous post has troubleshooting steps to start looking at your bridge circuit, but in addition I suggest a basic test of AIN2 & AIN4 where you remove your signals and instead jumper them to VS or GND and confirm the read 5V or 0V.

ed1
I ordered another U6 for

I ordered another U6 for spare and testing; I've identified that it would not work at BOTH (but separate signals) locations: AIN2_3 from "screw terminal edge" and AIN0_1 from DB37 at rear connection.  Could you shine some light on this?  - I understand the U6 did state not to use BOTH locations which I thought it meant don't use both AIN0_1 at front and back together.  Does this imply that when rear connectors are utilized the all front should not be??  by the way, I did use DAC1 at front and back locations together.  DAC1 voltage was reading as expected at both location ends...

(In case you're wondering, I had a custom cable made accessing the back but wanted to conveniently use the front AIN2_3 that is not connected in the custom cable.)

Thanks.

LabJack Support
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AIN0-3 appear the screw

AIN0-3 appear the screw-terminals and the DB37.  Both connections are the same thing, although on the U6 each has it's own series 2.2k resistor so they are not a direct short to each other.

You can connect to some of these on the U6 while some are connected on the DB37.  Nothing wrong with that.  It generally does not make sense to connect to the same analog input on the U6 and DB37 at the same time.

Do you have a CB37?  Use the Test panel in LJControlPanel to view the voltage readings from AIN0-3.  Remove all other connections from your U6 except USB and the CB37, and then securely install jumpers to VS or GND to the AIN screw-terminals on the U6 or CB37.  You should read 5V or 0V from each channel as expected.