I have two strain gauges (load cells OMEGA, LCM101-100). I am carrying out a practical using these two. But the lab environment has different humidities and temperatures at different times. I simply want to know which factor (temperature or humidity) makes my readings most susceptible for error? (Temperature changes from 20 - 25 celcius, Relative humidity changes from 60 - 90%)

What are your thoughts?

 

hi,
The LCM d/s gives the temperature effects.
E

 

I have two strain gauges (load cells OMEGA, LCM101-100). I am carrying out a practical using these two. But the lab environment has different humidities and temperatures at different times. I simply want to know which factor (temperature or humidity) makes my readings most susceptible for error? (Temperature changes from 20 - 25 celcius, Relative humidity changes from 60 - 90%)

What are your thoughts?

Humidity effects are rather slow and require the humidity to penetrate the epoxy that bonds the resistors to the base lever. Even the slight effect of the humidity swelling or weakening the epoxy are going to be very slight vs the temperature. Measure over several days, I doubt there is a correlation to humidity.

 

Humidity effects are rather slow and require the humidity to penetrate the epoxy that bonds the resistors to the base lever. Even the slight effect of the humidity swelling or weakening the epoxy are going to be very slight vs the temperature. Measure over several days, I doubt there is a correlation to humidity.

Thanks GopherT.

When my Air condition goes off, the readings actually go higher, but when it is with the air condition, the readings again come to the usual level.

That's why i am trying to relate this issue to Temperature or Humidity. I did the readings for several days. Same issue all along.

The only additional thing I can do, is to do my experiments in a controlled environment.

 

hi,
The LCM d/s gives the temperature effects.
E
View attachment 136957

Thanks for this E. But unfortunately im getting worse than these.

 

hi A,
How are you measuring the L/C performance.? are you sure it is not the measuring instrument or indicator thats being effected by the A/Con.?

E

 

Thanks GopherT.

When my Air condition goes off, the readings actually go higher, but when it is with the air condition, the readings again come to the usual level.

That's why i am trying to relate this issue to Temperature or Humidity. I did the readings for several days. Same issue all along.

The only additional thing I can do, is to do my experiments in a controlled environment.

If the aluminum load cell block is in the flow of air from the vent, it will experience a much wider temperature swing that your room thermostat sees. Aluminum is an excellent conductor of heat (cold) and incoming air from he vent is way cooler than room air.

 

Something you may want to look at is your excitation voltage, how stable is it with ambient temperature change? Additionally your actual strain gauge bridge output, does it remain stable with ambient air temperature change? Either the excitation supply voltage or the strain gauge bridge amplifier can induce errors with ambient air temperature change. I would look at those two parameters and take some notes across different ambient temperature change. Your excitation voltage needs to be very stable if you want repeatable measurements.

Ron

 

hi A,
How are you measuring the L/C performance.? are you sure it is not the measuring instrument or indicator thats being effected by the A/Con.?

E

Thanks E.
The load cells are connected to a panel meter D41-B. It only reads what L/Cs output. Thats why I think my L/Cs are faulty or too sensitive to temperature or humudity.

 

If the aluminum load cell block is in the flow of air from the vent, it will experience a much wider temperature swing that your room thermostat sees. Aluminum is an excellent conductor of heat (cold) and incoming air from he vent is way cooler than room air.

Thanks GopherT. Let me close all the air ducts around my rig area.

 

Something you may want to look at is your excitation voltage, how stable is it with ambient temperature change? Additionally your actual strain gauge bridge output, does it remain stable with ambient air temperature change? Either the excitation supply voltage or the strain gauge bridge amplifier can induce errors with ambient air temperature change. I would look at those two parameters and take some notes across different ambient temperature change. Your excitation voltage needs to be very stable if you want repeatable measurements.

Ron

Hi Ron,

Thank you for your update. I have configured the Panel Meter (DP41-B, Omega) in the bridge setup with 0-100 mV range. Im only guessing it is too sensitive. Is that the case? The excitation voltage is provided by the panel meter itself.

 

Hi Ron,

Thank you for your update. I have configured the Panel Meter (DP41-B, Omega) in the bridge setup with 0-100 mV range. Im only guessing it is too sensitive. Is that the case? The excitation voltage is provided by the panel meter itself.

The Omega Engineering DP41 meters are among the best out there for your application. I have used them in a wide range of industrial settings and they were rock stable. While not quite inexpensive they are a great meter and the excitation out in my experience has always been stable. The DP41 sort of just eliminated my two possible causes for your problem.

Hi Ron,

Thank you for your update. I have configured the Panel Meter (DP41-B, Omega) in the bridge setup with 0-100 mV range. Im only guessing it is too sensitive. Is that the case? The excitation voltage is provided by the panel meter itself.

I doubt it as your sensor sensitivity is 3 mV/V so with 10 Volt excitation a full scale output would be about 30 mV. You are using the 100 mV range.

Ron