CST Troubleshooting Techniques & Repair Methods 3

Question 1

When using a summing card (junction box) to diagnose individual load cells, what measurement confirms a shorted load cell?

Accepted Answer

Lower than specified bridge resistance

Answer

A shorted load cell will exhibit lower than specified bridge resistance because additional current paths reduce the effective resistance.

Question 2

A platform scale indicator shows 'ERR-2' and will not accept a zero command. According to typical manufacturer conventions, what does this type of error most likely indicate?

Accepted Answer

Weight is outside the acceptable zero range

Answer

Most scale indicators use error codes like 'ERR-2' or similar to indicate that the current weight is outside the permissible zero band for the zero command.

Question 3

A scale technician notices that a scale reads correctly in the morning but reads high by several graduations in the afternoon. What phenomenon is most likely responsible?

Accepted Answer

Thermal expansion of the platform structure causing mechanical stress on load cells

Answer

Thermal expansion of the platform during the warmer part of the day can induce mechanical stress on load cells, causing artificially elevated readings.

Question 4

When replacing a sealed load cell, a technician must apply sealant around the cable entry point. What is the primary purpose of this step?

Accepted Answer

To prevent moisture from wicking into the load cell along the cable

Answer

Sealing the cable entry prevents moisture from entering the load cell via capillary action along the cable, which would degrade insulation resistance and cause signal errors.

Question 5

A retail price-computing scale fails its shift test (constant load test). The reading drifts more than the permissible tolerance over 30 minutes. Which component is most likely to blame?

Accepted Answer

A load cell exhibiting excessive creep

Answer

The shift test measures reading stability over time under a constant load; excessive creep in a load cell causes the output to slowly drift and fail this test.

(CST) Certified Scale Technicians Practice Test

(CST) Certified Scale Technicians Practice Test

CST Troubleshooting Techniques & Repair Methods 3