CST Electrical Systems & Mechanical Components 3

Question 1

What is the purpose of a junction (summing) box in a multi-load-cell platform scale?

Accepted Answer

To parallel-connect load cells and trim outputs for equal contribution

Answer

A summing box connects multiple load cells in parallel and uses trim resistors to balance each cell's contribution to the total signal.

Question 2

A technician measures zero balance on a new load cell and finds it is -0.3 mV/V. This indicates:

Accepted Answer

A normal condition within typical ±1% rated output tolerance

Answer

Zero balance offsets of ±1% of rated output are standard and are corrected by the indicator's zero calibration function.

Question 3

Which mechanical symptom most likely indicates worn or damaged check rods on a vehicle scale?

Accepted Answer

Lateral movement of the deck when a vehicle drives on at an angle

Answer

Check rods (or stay rods) prevent lateral and longitudinal deck movement; wear allows the deck to shift sideways under off-axis loading.

Question 4

When using an ohmmeter to check a load cell, a technician measures 0 Ω between the signal+ and signal− terminals. This most likely indicates:

Accepted Answer

A short circuit within the load cell bridge

Answer

Signal terminals should show the bridge output resistance (typically 350 Ω or higher); 0 Ω indicates a short across the output arms of the bridge.

Question 5

Electrostatic discharge (ESD) protection in a weighing instrument is most effectively achieved by:

Accepted Answer

Properly bonding the instrument chassis to earth ground

Answer

Bonding the chassis to earth ground provides a low-impedance path for static charges to dissipate safely before reaching sensitive electronics.

(CST) Certified Scale Technicians Practice Test