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Using a S2M transducer to read force measurements. New to LabVIEW.

Hey!

 

My aim is to study the frictional force in an arm that is in touch with a 20N S2M force transducer. I have then connected the S2M in a full bridge configuration but since I inherited this machine I am not sure about the values to use as minimum and maximum in the force measurement. It says that the reading is 20N- 2 mV/V. Another question I have is how to setup a vi in LabVIEW to continuously record the force values using a NI 9219 reader and a cDAQ-9171 reader. I am new to LabVIEW so would appreciate all the help. Thanks :).

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Message 1 of 30
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Hi Vin,

 

To get started with the 9219, take a look at the Analog Input examples.

You can find examples by opening LabVIEW and going to Help > Find Examples...

 

If you don't know what you're looking for (usually the case) then use the search tab (not the directory layout).

Note you might sometimes have to scroll a lot, the search isn't amazing...

For your particular example, I'd suggest taking a look at something like "Voltage - Continuous Input".

 

2mV/V is your sensitivity, it tells you that at full scale (so 20N) you'll get an output of 2mV for each volt of excitation you supply to the bridge.

Since a typical excitation (from your power supply) might be ~10V, that's only 20mV...

 

Usually you also use an amplifier to increase this value before digitizing the result. So force transducers include an amplifier, some do not.

Depending on your accuracy requirements, this might be more or less required (but probably it is required).

Some NI modules are specifically designed for measuring bridge configurations, but the 9219 is not one of them (this doesn't mean it won't work - just that you'll need to provide a suitable input, and 20mV at full scale probably isn't enough to have good resolution assuming you're wanting variation in output with varying force 😉 )


GCentral
Message 2 of 30
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Hey!! Thanks for the detailed response! Yes I found an example which uses a Bridge configuration to give the force continuously. However I'm not observing peaks when I got the force transducer. Would this be due to the resolution problem that you suggested? Should I go for a more narrow resolution? Also would you suggest that I buy a new receiver rather than the 9219?

 

One last question that I have is at the moment I am not using an amplifier as I'm connecting the force transducer directly to the 9219. Do you think it's 100% necessary to get an amplifier?

 

Regards,

Vin

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Can you upload the datasheet for the sensor? The manufacturer requires registration to download it.

 

I'll check the NI module and give some examples for resolution later (on phone now) but you can probably reduce the max values (and increase min, because they are by default +-10V) to slightly improve your resolution. The NI datasheets usually give some example figures but I haven't checked the 9219 module's yet.


GCentral
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Message 4 of 30
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Hej,

 

Ok I will wait for your reply. Thanks again for the help! I have attached the datasheet of the force transducer with this reply.

 

 

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Message 5 of 30
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Hi Vin,

 

the NI9219 datasheet shows you can use in input range of ±7.8mV/V for fullbridge-type sensors like yours with a 24bit ADC, so you will not need an additional amplifier…

 

(It might be hard to find an amplifier with better accuracy than your class 0.02 sensor.)

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
Message 6 of 30
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Hey ok thanks! That is good to know. I have connected in a full bridge setup and I am using the continuous bridge vi that I have attached with this post. However I am not seeing significant deflections in the force if I hit the force transducer with a hammer or something. What do you think could be the reason for this?

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Message 7 of 30
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Hi Vin,

 


@Vin91 wrote:

I have connected in a full bridge setup and I am using the continuous bridge vi that I have attached with this post. However I am not seeing significant deflections in the force if I hit the force transducer with a hammer or something. What do you think could be the reason for this?


There can be many reasons…

 

Does the VI show the settings as you used with your sensor? (Which settings do you use?)

What are "significant defelctions"? What kind of signal do you get?

Is the wiring to your sensor done correctly?

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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Message 8 of 30
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Hi,

 

So my settings are Full bridge with a bridge resistance of 350 ohm. My range is first value 0 corresponding to 0N and second value 2mV/V corresponding to 20N. Then I plotted a continuous waveform graph where the amplitude constantly wavers between - and + 0.02 in amplitude. However when I hit the sensor with a hammer, I am not always observing a rise in the amplitude value.

I am however not 100% certain regarding the wiring. From what I have understood it is in the full bridge configuration but the terminologies used by NI and the sensor manufacturers are slightly different.

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Message 9 of 30
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Hi Vin,

 

are you any excitation? External or internal excitation? Which excitation value?

Which sample rate?

 

(You might set your typical settings and choose Edit->Set current values as default from the menu. Then save the VI and attach it again…)

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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