Question

If an instrument produces the same reading at different times for the same variation in the measured variable, then it is said to

• A. Have no hysteresis
• B. Have no accuracy
• C. Have no dead zone
• D. Have no drift

Hint:

Think about each term in the context of a graph of output versus input over time. Hysteresis would show different paths for increasing and decreasing input. Drift would show the entire output curve shifting over time for the same input. Dead zone would show a flat region where input changes don't affect output.

Answer 1

The Correct Option is D

Step 1: Understand the definitions of the given terms related to instrument performance.
Hysteresis: This is the phenomenon in which the value of a physical property lags behind changes in the effect causing it. In measuring instruments, hysteresis means that the reading obtained depends not only on the current value of the measured variable but also on its past values and the direction of change. For example, the reading might be different when the measured variable is approached from a higher value versus from a lower value. Accuracy: Accuracy refers to how close the reading of an instrument is to the true value of the measured variable. An instrument can be precise (consistent readings) but inaccurate (far from the true value). Dead zone (or Dead band): This is the range within which the input variable can change without causing any change in the output reading of the instrument. An ideal instrument has no dead zone. Drift: Drift is a gradual and unwanted change in the output reading of an instrument over time, even when the input variable remains constant. It can be caused by factors like temperature changes, aging of components, or variations in power supply. Step 2: Analyze the condition described in the question.
The question states that the instrument produces the same reading at different times for the same variation in the measured variable. This implies that the instrument's reading is consistent over time for a given input change. Step 3: Relate the described condition to the definitions of the instrument performance terms.
If the instrument had hysteresis, the reading for the same value of the measured variable might be different depending on whether the variable was increasing or decreasing. The question implies consistent readings for the same variation, regardless of when it occurs relative to other variations. Accuracy is about how close the reading is to the true value, not about the consistency of readings over time for the same input variation. The instrument could be inaccurate but still produce the same reading at different times for the same input change. A dead zone would mean that small changes in the measured variable do not result in any change in the reading. The question talks about the same reading for the same variation, implying that the instrument is responding to changes. Drift refers to a change in output over time for a constant input. The question states that for the same variation in the measured variable, the instrument gives the same reading at different times. This suggests that the baseline or the response to a change is not shifting over time, which is the absence of drift. Step 4: Conclude the property of the instrument based on the given condition.
The fact that the instrument provides consistent readings over time for the same changes in the measured variable indicates that its output is stable and not subject to unwanted gradual changes when the input variation is the same. This is the characteristic of an instrument that has no drift.