User manual

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USB DrDAQ User's Guide 31

Offsets

The above linear and non-linear responses could have a voltage, current, resistive or

other type of offset that may need taking into account. It is quite usual to see offsets

in output signals from sensors.

Sensor output

The USB DrDAQ requires an input signal in DC volts or resistance. The sensor in

question could give an output in other units such as resistance, current or AC volts.

Drift

It is possible that the sensor output drifts over time. This may involve recalibration of

the sensor at set time intervals, or some self-calibration.

Hysteresis

The sensor may give a different output value when rising to a voltage than when

falling to a voltage. This is difficult to eliminate and should be taken into account.

Once the sensor has been selected and all of the above has been considered, the

design of some scaling circuitry can begin. There are many ICs on the market that can

be purchased cheaply that deal with the above potential problems. Look into these

before re-inventing the wheel and spending expensive development time designing a

circuit that can be purchased for a few pounds.