How to connect quarter bridge strain gauge connection and take measurements in uE? do you have video?

I have connected a strain gauge to channel 4. in configuration, I have added current bridge, selected appropriate current bridge and channel. After downloading the data I have got a value of 500,930.5. this is a huge value.

If I press the strain gauge I can see the variations however, the data in the range 500,930.5 I high, how to make it zero and the get the values in uE?

Good evening,

Do you have a bridge completion resistor in the lower half of the bridge?
Usually when the readings are out by so much it is because the resistor has been left off or isn't commented correctly

Also look at the FAQs for details on converting from PPM to ue

Cheers,
Roger

You mean RC in the diagram as bridge completion resistor? If yes, I didn't connect that one. I thought it is a wire resistance mentioned like that. what value resistor I have to connect? it should be the same value of active strain gauge?

Hi senthilkumaranms,

Yes RC is the bridge completion resistor and you need to use the same value as your strain gage.

Best regards,
Rudy Gunawan

Good morning senthilkumaranms,

To add a bit more detail and clarify.

For 1/4 bridge configuration
Rc is either
1/ Strain gauge bridge completion resistor with R being the same value as you strain gauge.
These bridge completion resistors must have very high temperature stability (Typically 1PPM per deg C) and an accuracy of +/- 0.01 %
2/ A strain gauge that under goes the same thermal history as the gauge of interest but is not strained. This will provide temperature compensation.

For a half bridge then use a gauge in place of Rc and it must see a strain in the opposite sense to the top gauge

Cheers,
Roger

Today I have connected as suggested in this forum and applied the calculation (4/(21))("Strain") ("Strain" is the name assigned to the channel)to get uE from the raw measurement. now I am getting the values in the range of 5000 uE initial undisturbed condition. But I am seeing lot of fluctuations of 200 -300uE in undisturbed condition. How to check the strain value is correct and why there is huge fluctuation. I am testing in laboratory where there is no temperature variations and connection are perfect.

I have connected 80.8k shut resistance to check my strain measurements. for 80.8k shunt resistance, I have to get 740uE.
Raw Measurement
Initial value = -2028 UE
shunt calibration = -1217 uE
Diff = -2028 -1217 = 800 uE

After applying calculation all the values are doubled which is incorrect. in the manual, whatever calculation is given I have applied it but the values are wrong. raw measurement itself is close to calculated strain value.

Now I am having two problems

• If calculation is applied I am getting incorrect values
• Fluctuations in strain 200 - 300 uE undisturbed condition.

Please give your suggestion.

Good morning senthilkumaranms,

You are using the formula for a full bridge
Please use (2/(Gauge factor1))PPM for the half bridge

Cheers,
Roger

Can somebody help me reducing the fluctuation?

Can I connect strain gage pasted in one dummy specimen to all the strain channels for bridge completion?

Good morning senthilkumaranms,

No you can't use one gauge for all completion.
If is VERY important that the dummy gauge sees the same thermal history as the gauge being measured.

On the fluctuation problem, What is the value and tolerance of the bridge completion resistor you are using?
Typically a bridge completion resistor is say 350 Ohms +/- 0.01% and 1 PPM per deg C. any thing less and you will see fluctuations due to temperature etc.

Cheers,
Roger

In a controlled room, such a fluctuation is very high. another thing what I noticed is If I touch the DAQ body, strain values and all other sensor values whatever connected in DAQ is varying heavily. I have done the ground connection also. still variations in strain measurements is very high.

as mentioned by you, if it is because of temperature effect on completion resistor, it is applicable for quarter bridge sensors. but I am seeing fluctuations even in fully bridge sensors like load cell. PPM values varying between 2000 - 10000.

Load cells can be used to connect these products.On the fluctuation problem, What is the value and tolerance of the bridge completion resistor you are using? load cell sensors can play a very vital role in connecting process !

Good morning aparkfind,

Then you either have a grounding problem, wiring issue, or there is a lot of noise on the power line.

Being a control roll i suspect that it may be a power quality problem.
Try running the dataTaker on a battery, then plug in the power supply. If there is no noise on the battery and noise on the mains then you need a power conditioner.

Cheers,
Roger