CWT Weighing System Installation & Verification 1 — Questions and Answers
Question 1: What is the primary function of a check rod (stay rod) in a hopper or tank scale installation?
- To prevent lateral movement while allowing vertical load measurement (Correct answer)
- To provide an electrical ground path for the load cells
- To offer additional vertical load-bearing support to the structure
- To interconnect multiple load cells electrically in the network
Correct answer: To prevent lateral movement while allowing vertical load measurement
Check rods constrain horizontal and lateral movement of the vessel without interfering with the vertical forces the load cells must measure.
Question 2: Which type of fastener is recommended when mounting load cells in environments subject to vibration?
- Standard hex bolts with flat washers
- Nylon insert lock nuts (Nylock) or prevailing torque fasteners (Correct answer)
- Self-tapping sheet metal screws
- Eye bolts secured with cable ties
Correct answer: Nylon insert lock nuts (Nylock) or prevailing torque fasteners
Nylon insert lock nuts (Nylock) and other prevailing torque fasteners resist loosening caused by repeated vibration, maintaining proper load cell clamping force.
Question 3: What is the typical rated output of a standard strain-gauge load cell at full capacity?
- 0–10 V DC
- 4–20 mA
- 2–3 mV/V (Correct answer)
- 0–5 V DC
Correct answer: 2–3 mV/V
Standard strain-gauge load cells produce a millivolt-level differential signal, typically rated at 2–3 mV/V of excitation voltage at full rated capacity.
Question 4: During weighing system installation, which environmental condition most critically affects measurement accuracy?
- Ambient lighting levels in the installation area
- Temperature stability and thermal gradients across the structure (Correct answer)
- Background noise levels from nearby machinery
- Atmospheric pressure at the installation site
Correct answer: Temperature stability and thermal gradients across the structure
Thermal gradients cause differential expansion of the weighing structure and shift load cell zero and span, making temperature stability the most critical environmental factor.
Question 5: What tool is used to verify that a platform scale is properly leveled during installation?
- Laser distance measurer
- Spirit level or precision machinist's level (Correct answer)
- Calibrated torque wrench
- Digital multimeter
Correct answer: Spirit level or precision machinist's level
A spirit level or precision machinist's level is placed on the platform surface to confirm it is within the allowable tilt tolerance before calibration begins.
Question 6: Why is shielded cable required for load cell signal wiring in most installations?
- To boost the millivolt signal to a higher voltage level
- To prevent electromagnetic interference (EMI) from corrupting the low-level signal (Correct answer)
- To allow cable runs longer than 100 feet without additional amplifiers
- To meet NEC requirements for wet-location wiring
Correct answer: To prevent electromagnetic interference (EMI) from corrupting the low-level signal
Load cell signals are in the millivolt range and extremely susceptible to EMI; shielded cable with the shield grounded at one end prevents induced noise from corrupting the measurement.
Question 7: When installing a truck scale, which foundation characteristic is most critical for long-term weighing accuracy?
- Foundation surface color and anti-slip finish
- Concrete compressive strength and uniform bearing capacity (Correct answer)
- Foundation depth equal to the local frost line only
- Foundation width matching the scale platform width exactly
Correct answer: Concrete compressive strength and uniform bearing capacity
Adequate concrete compressive strength and uniform bearing capacity prevent differential settling that would shift load distribution among load cells and cause persistent errors.
CWT Weighing System Installation & Verification 1
What is the primary function of a check rod (stay rod) in a hopper or tank scale installation?