Hi,
If you need temperature stability, then a full bridge is best.
There are signal conditioning ICs especially made for strain gauge applications.
What do you want to calibrate? Gain, offset? In whag range?
What precision do yo want? ( Yes, I know you like to answer: The best one can achieve.. But with this answer nobody can calculate. We need values)
Klaus
This means laser calibration of the applied strain gauge. Very difficult and high effort.i need to do a calibration that the V+ and V- differential voltage will be 0V when is no tension
This is totally different. Use any ADC, measure the initial value and store this value in an EEPROM.i need only to sense the change in tension
Hi,
Two different things.
This means laser calibration of the applied strain gauge. Very difficult and high effort.
This is totally different. Use any ADC, measure the initial value and store this value in an EEPROM.
You need to define what accuracy, what precision and what resolution you want. (No text. Values)
Pleas give more information.
How many sensors? How often do you need/read/store a value? Mobile or stationary solution. What power supply, what communication?
Tell us more.
Klaus
Hi,
* With three states: you need no precision. You even don´t need to worry about temperature drift.
* With a microcontroller you don´t need to calibrate on the analog side. Do it with software. It is more easy.
* Just use a simple OPAMP circuit to amplify the signal. Add a C for low pass filtering.
Klaus
Hi,
some questions:
* Does your ADC provide differential measurement?
* what is the max expected strain gauge output signal range (including offset)?
* what is the (decoded) max. ADC input range ("differential" input range, if possible)?
Klaus
Hi,
your circuit is incomplete. There are no gain setting resistors.
Could you use a second ADC_input to act as differential input? (connected and read_out independently- interleaved-, but subtracted in your software)
There are many possible solutions.
For a single ADC input solution maybe an instrumentation amplifier is a good choice. Set the output offset to ADC_range/2.
***
In any case:
* use low pass filters for the strain gauge signal
* and for the VRef
Both need to have the same characteristic and fc.
Klaus
Hi,
there are ready instrumentation opamps.
in sloa034.pdf see Figure5.
Please change: connect R3 to ADC_input_range /2 (instead of GND)
(Maybe use two equal resistors with twice the initial value of R3. Connect one to GND and the other to VRef)
I think this is a simple and good solution. Using only one ADC input.
Klaus
Hi,
I can´t say anything about the strain gauge.
But the electrical parameters seem to be good.
Expect a 10mA of strain gauge current. Making 33mW of disspated power.
***
About the instrumentation amplifiers:
I didn´t check them. But your application ist not that critical, so I assume all will work.
***
About the circuit.
Yes this is a good solution.
To suppress 3V3 noise you need to add a second LPF from VCC to VREF.
Only if both filters have the same characteristic the errors are compensated.
An unfiltered VRef generates the same error as an unfiltered signal.
good luck.
Klaus
Because the ADC_Vref is 1.8V also the digital output of the ADC won´t change. --> The ADC value is independent of VCC, it is proportional to the tension.For better power dissipation i can work with 1.8V ( all the components can work with this voltage) but it will cause a minor change in voltage( when tension applied on the bridge) at the bridge output and ill be more sensitive to noise.
That´s what i wrote:you told me that i will not need to calibrate the bridge
--> if you want to calibrate for offset, then just subtract a constant value. Usually stored in the EEPROM. It can be initiated with a key press.* With a microcontroller you don´t need to calibrate on the analog side. Do it with software. It is more easy.
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