Adjustable encoder can have the effect of position sensor, the circuit can be properly adjusted.
Adjustable encoder is the most appropriate is used as a voltage divider.
Adjustable encoder can also act as a variable resistance, however at this time there are some potential pitfalls.
Do you know the difference between the two functions?
ACTS as a divider adjustable encoder, absolute value encoder will not affect the output voltage.
Between the input voltage and output voltage is proportional to.
Commonly used encoder has poor resistance accuracy and low temperature coefficient.
Resistance even, but as long as encoder, no matter what or the temperature coefficient of resistance precision will share in the location of the 30% 30% of the voltage.
Assumes that the sliding vane and high impedance circuit connection, contact resistance of sliding vane will not affect the output voltage.
Sliding vane is sliding vane contact resistance and resistance element resistance on the contact point.
As shown in figure 2, when the adjustable encoder ACTS as a variable resistor, it will affect the precision of resistance and temperature coefficient circuit.
Sliding vane will affect the circuit resistance, contact resistance and contact resistance sliding vane resistance will position, temperature, vibration and changes with time and change.
Sometimes variable resistance is necessary, can work under the mode of the proportion of coder to design a variable resistor.
Two circuit shown in figure 3 has a similar function.
Figure 3. A use P1 as a variable resistance, in the output of U1 voltage produced a reverse phase voltage with a linear relationship with the encoder position.
Due to the resistance changes of P1 range is very large, so by R3 to achieve gain control.
In addition, the output voltage and the encoder position between linearity and repeatability will be affected by the sliding vane contact resistance.
Operational amplifier is introduced in figure 3 b U2, makes the encoder work in proportion model, which can eliminate defects in figure 3 a.
Operational amplifier U2 provides high input impedance so as to reduce the influence of contact resistance.
As the encoder position changes, operational amplifier between U2's output voltage from 0 v to Vref change accurately.
To operational amplifier U3 provides an accurate voltage range, and thus need to R5, R6 set a fixed value, and does not need to gain control circuit.
Work in order to make the adjustable encoder encoder in proportional mode, if you need extra operational amplifier circuit or higher complexity?
This is need you to make a tough decision.
Sometimes can't avoid the encoder as a rheostat.
But through the understanding of risk factors and sensitivity, you can choose the encoder to meet the required performance.
And you will know when circuit test certification to pay special attention to problems that may occur.
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