Re : I can not measure strain gauge

[immortal]

I have not solve this noise problem yet. There is a noise which affects output of the strain gauge adding 50Hz line frequency and this effect is multiplied with 100 in the SCC-SG04 as given in figs of the previous message.  

Is there anybody that experienced with the noise problem like me?

How can I change the excitation voltage source as "external excitation" in the MAX?

Thank you for your attention.

Kemal

[Hani R]

Hi Kemal,

You can use an SCC-LP low pass filter module in series with the SCC-SG04, to remove unwanted frequency components. To get rid of the noise, you may consider using a lowpass filter module. 

As for the error you get when configuring the Strain Gauge task to use external excitation, I have reported the issue to R&D (4GJ7C44I) for further investigation.  I'm sorry for the inconvenience and I will certainly post if I get any new information. 

[Wilfried_71]

Is your noise appear when you plug your externel power supply of 10 V (in comparison with the internal power of sg04) ? Is your externel power supply a special supply for strain gage measurement ?

Because you must take a very good regulated power supply in order to have not noise on the record signals ... And I always think that your sensor MUST be work with the internal power of 2.5 V.

[immortal]

Hi Hani R.,

I have no chance to to buy SCC-LP module. I will consider to amplify +2.5 internal excitation using non-inverting op-amp circuit (low noise) for excitation voltage. I hope it works.

There is no solution with working external excitation as far as I understand for now.

I have a question with NI6221 DAQ card. I want to decrease AI input range to gain higher resolution. I modify AI min-max input range as [-100m,100m] in NI6221 AI test tab for this purpose. Go to my strain task and test the modification result but there is no change. How can I modify input range of stated AI?

Thank you for your help.

Kemal

[immortal]

Hi Wilfried,

With SG04 there are some noise but it have not regular shape like sine wave, really randomly distrubuted :). Noise appears when I connect a cable with the length of 20-30cm to excitation terminal of strain gauge. Not the external power supply have connected yet. I suppose that this cables gathers EM waves in the environment.

My sensor is working with +2.5V excitation voltage but I can not see big changes when I gently push the load cell (2kg capacity) with my finger and the noise is comparable high.

Best regards.

Kemal

[Wilfried_71]

Is your wire shielded ? It's recommended to select a such wire. Do you have a electric motor working or a magnetic system closed to your acquisition ? It can be the cause of a lot of problem.

For the signal changes when you touch the sensor, do you try to software amplify the signal ? For example in Labview; you multiply the waveform by a factor of 500000 for example to try to see a change ?

Is your sensor working properly with an other conditioning box ?

[Mark_E]

Hi immortal,

You said you pressed it intensively (11/14/07) and it may have been damaged. Do you have a different load cell you could try? Or as Wilfried_ARM asked, have you tried it on another setup?

When using a task, the DAQ card automatically sets its input range to the smallest value based on the actual voltage returned by the strain measurement. Changing the range in the test panel will not affect any other tasks; just the raw measurements acquired without other tasks.

[immortal]

Dear Wilfried,

Wires are not shielded. I use the signal conditioner close to desktop PC but there is no change in noise level when I take Sig.Cond. away from my PC.

I tried to amplify the signal in Labview but I have not succeeded. I see small changes in Labview strain gauge measurement example but it need to be enlarged. I have connected the obtained data to multiply with a constant multiplier but constituted constant is not a scalar, it have a structure including DD.MM.YYYY format. I have not understand why this data structure is occured because I haven't dominated Labview yet :(.

I have not tested the load cell with other cond. boxes but my sensor is working because I have tested the other tree load cells also and they give same characteristics.

[immortal]

Dear Mark E.

I have tried with three other load cells and there is no change. If I damaged the load cell is it gives output changes? My strain read system is given in Fig 1. In Fig 2 and 3, the outpus of the system for the cases of no-load and load (finger press). Obtained amplitude is still low for load mode. Can I change the input range of AI channel in Labview?

Best wishes

Kemal

[immortal]

Sorry for Fig 1. I changed it again.