CST CST Environmental Factors & Scale Performance 1 — Questions and Answers
Question 1: How does a significant temperature change typically affect a load cell's output reading?
- It has no measurable effect on calibrated digital load cells
- It causes a shift in both zero and span due to thermal expansion and changes in strain gauge sensitivity (Correct answer)
- It only affects the scale indicator display, not the load cell signal
- It only increases the load cell's rated capacity
Correct answer: It causes a shift in both zero and span due to thermal expansion and changes in strain gauge sensitivity
Temperature changes cause thermal expansion in the load cell body and alter the piezoresistive sensitivity of the strain gauges, shifting both the zero balance and span calibration.
Question 2: What is the purpose of a temperature compensation circuit built into a load cell?
- To actively heat the load cell in cold weather conditions
- To minimize the effect of temperature changes on the load cell's output signal accuracy (Correct answer)
- To prevent condensation from forming on the load cell housing
- To regulate the operating temperature of the scale indicator
Correct answer: To minimize the effect of temperature changes on the load cell's output signal accuracy
Temperature compensation circuits use thermistors or precision resistor networks to counteract zero and span shifts caused by temperature changes, maintaining accuracy across the specified temperature range.
Question 3: What is the typical operating temperature range specified for most commercial industrial scale load cells?
- -50°C to +100°C
- -10°C to +40°C (Correct answer)
- 0°C to +20°C only
- -100°C to +200°C
Correct answer: -10°C to +40°C
Most commercial scale load cells are specified for -10°C to +40°C operating range, covering typical indoor and outdoor commercial environments without extreme cold storage or high-heat industrial conditions.
Question 4: How should a scale be handled after being moved from a cold storage area to a warm room before calibration?
- Calibrate immediately while the load cell is still cold for best accuracy
- Allow the scale to fully acclimate to the ambient temperature before calibrating (Correct answer)
- Increase the span setting by a fixed percentage to compensate for temperature
- Replace the load cell since thermal shock may have damaged it
Correct answer: Allow the scale to fully acclimate to the ambient temperature before calibrating
Allowing the scale to acclimate prevents thermal gradients within the load cell from causing temporary measurement errors that would result in an inaccurate calibration.
Question 5: What effect does direct sunlight have on an outdoor truck scale platform during summer operation?
- No measurable effect since steel is a good thermal conductor
- Uneven thermal expansion of the steel platform stresses load cells and shifts zero readings (Correct answer)
- It improves accuracy by drying any moisture from the platform surface
- It increases the platform's effective capacity rating
Correct answer: Uneven thermal expansion of the steel platform stresses load cells and shifts zero readings
Direct sunlight heats the steel platform unevenly, causing differential thermal expansion that introduces stress on the load cells and shifts the zero reading on outdoor truck scales.
Question 6: What is 'thermal zero drift' as specified in a load cell datasheet?
- A calibration technique for correcting zero at elevated temperatures
- The gradual shift in the zero output reading per degree of temperature change (Correct answer)
- A type of mechanical failure mode caused by overheating
- An error code displayed when the load cell overheats
Correct answer: The gradual shift in the zero output reading per degree of temperature change
Thermal zero drift is the change in the load cell's zero output per degree of temperature change, expressed as a temperature coefficient in the load cell's specification datasheet.
CST CST Environmental Factors & Scale Performance 1
How does a significant temperature change typically affect a load cell's output reading?