Transducers in Measurement Questions and Answers

Answer: C

The cement transmits the strain of the surface to the gauge, so the gauge undergoes the same strain as the material beneath it. An unbonded gauge instead has wires stretched between insulating supports and is used in transducers rather than on structures.

Answer: D

The dummy is identical to the active gauge and mounted on the same material at the same temperature but unstrained. Placed in the adjacent bridge arm, its resistance change with temperature matches that of the active gauge and cancels in the bridge output.

Answer: A

One gauge on the top surface goes into tension and one on the bottom into compression, and placing them in adjacent arms doubles the output while cancelling any change common to both, temperature included. A full bridge with four gauges doubles it again.

Answer: B

The common thermistor has a large negative temperature coefficient and a markedly nonlinear characteristic. That gives a large signal over a narrow range, whereas a platinum resistance thermometer is nearly linear over hundreds of degrees but changes only slowly.

Answer: C

Platinum is chemically inert, may be obtained very pure and has a resistance-temperature relation so reproducible that it defines the international temperature scale over a wide range. A hundred ohm element at zero degrees is the usual form.

Answer: D

The element is a resistance carrying the measuring current, so it dissipates a little power and sits slightly above the temperature it is meant to report. The remedy is to keep the current small, which conflicts with wanting a usable signal.

Answer: A

A hundred ohm element changes by less than half an ohm per degree, so a few ohms of lead resistance is a large error. Extra conductors let the lead resistance be measured and subtracted, or excluded altogether by a four-terminal arrangement.

Answer: B

Correct answer: linear variable differential transformer

Each word describes the device: it measures *linear* displacement, its output *varies* with that displacement, the two secondary windings are connected in opposition so the output is a *difference*, and the whole is a *transformer* with a movable core. The name is worth unpacking because it also states how the instrument works.

Answer: C

With the core central the coupling to each secondary is equal and their opposed voltages cancel, so the null is a genuine electrical zero. A small residual voltage remains from imperfect symmetry and stray capacitance, and it is the limit on the device's resolution.

Answer: D

The magnitude tells how far the core has moved and the phase, in step with the primary on one side and reversed on the other, tells which way. A phase-sensitive detector therefore yields a direct voltage that is both signed and proportional.