Instrumentation amplifier
Amplifier module for instrumentation with impedance adapter function between sensors and transducers for automation (high impedance) and the input of the A / D section of the Microcontrollers (low impedance)
Technical features
- Gain: adjustable from 1 to 100 with resistive attenuation network and fine trimmer adjustment
- Input impedance:> 100 MOhm
- Output Impedance: <10 Ohm
- Common mode rejection:> 80 dB maximizable by trimmer
- Power supply: symmetrical, -12V 0 + 12V
- Dimensions: 65 x 50 mm
- Printed circuit: single-sided with tinned copper to MIL standards
- Connectors: 9-pole screw terminal block for power supply, input and output
- Applications: signal conditioning for interfacing sensors and high impedance transducers
- Available on request as a mounting kit or even just the C.S.
Design parameters
10k
Gain: Av = 2 * ( 1 + ------- )
R1
Output voltage: Vout = Vin * Av + Voffset (IC1-7)
Amplifier Calibration Procedure
The ELC-324 amplifier can be calibrated with regard to offset and gain, in order to obtain the desired minimum and maximum output values, in relation to the minimum and maximum input values provided by the transducer. With reference to the layout of the board, the iterative procedure for the calibration of the ELC-324 amplifier is as follows:
1) To maximize common-mode rejection (* max common-mode voltage = (+ VCC - 1) / 2):
- short-circuit the two input lines Vin + and Vin- and bring them to voltage + 5V (*)
- adjust R10 so as to obtain 0V on PIN 7 of IC1 (offset = 0)
- adjust R5 to obtain Vout = 0V
2) To adjust the offset:
- remove the previous short-circuits
- As a pre-adjustment, if you know the offset value of the transducer to be compensated and the gain, you can adjust R10 so as to obtain on the PIN 7 of IC1 a voltage value equal to: (offset * gain). if the transducer supplies a signal in the -1V + 1V range, which you want to translate at the output in the 0 - 5V range, then since in this case you have the values: offset = (0 - (- 1)) = 1; gain = (5-0) / (1 - (- 1)) = 2.5 then the value Voff = 1 * 2.5 = 2.5V is obtained for the voltage on PIN 7 of IC1.
- If the above values are not known exactly, or if a verification of the theoretical calibration is desired, it is necessary to carry out the following steps: apply the input signal having the minimum value adjust R10 until Vout is obtained with the desired value
3) To adjust the gain:
- apply the input signal having the maximum value
- adjust RP until Vout with the desired value is obtained.
To obtain maximum precision, it is advisable to repeat step 2 after performing step 3, repeatedly for various iterations, due to the interdependence between the two adjustments.