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Null type recorders are
bridge recorders.
LVDT recorders.
potentiometric recorders.
any one of the above.
potentiometric recorders.
Quick Summary: Null type recorders operate on the principle of a balancing mechanism where the unknown input signal is compared against a known reference signal. When the two signals are equal (the 'null' condition), the difference becomes zero, and the balancing system stops, indicating the measured value.
Null type recorders operate on the principle of a balancing mechanism where the unknown input signal is compared against a known reference signal. When the two signals are equal (the 'null' condition), the difference becomes zero, and the balancing system stops, indicating the measured value.
VerrorтАЛ=VinтАЛтИТVrefтАЛ=0
In a potentiometric recorder, an error signal is generated from the difference between the input voltage and a reference feedback voltage from a calibrated potentiometer. This error is amplified and used to drive a servo motor that adjusts the potentiometer wiper until the error is reduced to zero. Because the measurement is based on a zero-difference state, the system is independent of the absolute gain of the amplification stage, resulting in high accuracy.
Null-type recorders use an electromechanical balancing system.
They provide higher accuracy compared to deflection-type recorders as they do not load the source.
The 'Null' refers to the state where the error signal in the loop is zero.
Potentiometric recorders are the most common industrial application of null-type systems.
High accuracy due to the null-balance method.
Independent of supply voltage fluctuations due to differential comparison.
Provides high input impedance.
Slower response time compared to deflection-type instruments.
More complex mechanical construction (servo systems).
Prone to mechanical wear in the potentiometer/servo link.
Precision industrial temperature recording.
Laboratory-grade pH measurement and chemical analysis.
Strain gauge measurement systems.
Deflection-type recorders rely on the output proportional to input (e.g., analog meter needle deflection).
Null-type systems rely on maintaining the system at balance, essentially comparing the input to an internal standard.
C is correct тАФ Potentiometric recorders utilize a null-balancing technique to equate an unknown input voltage to an internal reference voltage.
Always remember that 'Null-type' denotes balancing to zero, whereas 'Deflection-type' measures based on the displacement produced by the quantity being measured.