Example D: Null measurements 3. MEASUREMENT METHODS. 3.1. Deflection, difference, and null methods Example D: Null measurements Let us first define some new terms that describe the interface of a measurement system: transducer is any device that converts a physical signal of one type into a physical signal of another type, measurement transducer is the transducer that does not destroy the information to be measured, input transducer or sensor is the transducer that converts non-electrical signals into electrical signals, output transducer or actuator is the transducer that converts electrical signals into non-electrical signals. Reference: [1]

Input transducer (sensor) 3. MEASUREMENT METHODS. 3.1. Deflection, difference, and null methods Example D: Null measurements Input transducer (sensor) Non-electrical signal Sensor Electrical signal ES N-ES

Output transducer (actuator) 3. MEASUREMENT METHODS. 3.1. Deflection, difference, and null methods Example D: Null measurements Output transducer (actuator) Electrical signal Actuator Non-electrical signal N-ES ES

Measurement system interface 3. MEASUREMENT METHODS. 3.1. Deflection, difference, and null methods Example D: Null measurements Measurement system interface Measurement System Sensor Actuator Non-electrical signals Non-electrical signals Sensor Actuator

Example D: Null measurements 3. MEASUREMENT METHODS. 3.1. Deflection, difference, and null methods Example D: Null measurements Our aim in this example is to eliminate temperature drift in the sensitivity of a dc magnetic field sensor with the help of a linear temperature-insensitive reciprocal actuator. Ha VS Vo Hact Sensor Actuator Vs Hact T1 T1 T2 T2 Ha Vo

Example D: Null measurements 3. MEASUREMENT METHODS. 3.1. Deflection, difference, and null methods Example D: Null measurements Sensor Hact VS Ha A= Vo Null detector Reference (Helmholtz coils) VS  0 Io Any ideas? VS Hact=Ha T1 The sensor temperature-drift errors and nonlinearity are not important T1 T2 Hact 1=Hact 2 T2 DH=Ha -Hact Vo 1=Vo 2 Vo DH1=DH2 =0

Example E: Difference measurements 3. MEASUREMENT METHODS. 3.1. Deflection, difference, and null methods Example E: Difference measurements Reference (Helmholtz coils) Io Hact G AOL 1+AOL b Hact =Ha _______ VS Sensor Vo VS > 0 A< Ha VS Hact T1 The sensor temperature-drift errors and nonlinearity are important T1 T2 Hact 1 VS 2 T2 Hact 2 VS 1 DH=Ha -Hact Vo 2 Vo 1 Vo DH1 DH2