RPLS Equipment and Tools Knowledge 2 — Questions and Answers
Question 1: What is the primary purpose of a tribatch (tribrach) on a surveying instrument?
- To measure vertical angles
- To level and center the instrument over a point (Correct answer)
- To amplify the telescope magnification
- To record electronic distance measurements
Correct answer: To level and center the instrument over a point
A tribrach is a leveling base that allows the instrument to be precisely leveled and centered over a ground point using leveling screws and an optical plummet.
Question 2: Which type of EDM (Electronic Distance Measurement) uses a modulated infrared or laser beam reflected by a prism target?
- Microwave EDM
- Electro-optical EDM (Correct answer)
- Ultrasonic EDM
- Inertial EDM
Correct answer: Electro-optical EDM
Electro-optical EDMs use modulated light (infrared or laser) reflected from a retroreflective prism to measure distances based on phase differences.
Question 3: A surveyor notices the bubble in the plate level of a total station drifts consistently to the same side after rotating 180°. This indicates:
- The instrument is set up on unstable ground
- The plate level vial needs adjustment (two-peg test error) (Correct answer)
- The optical plummet is misaligned
- The vertical circle index error is too large
Correct answer: The plate level vial needs adjustment (two-peg test error)
When the bubble displaces by the same amount after a 180° rotation, the vial axis is not perpendicular to the vertical axis and requires adjustment.
Question 4: What does the term 'stadia' refer to in traditional surveying?
- A method of measuring horizontal distances using crosshair intercepts on a rod (Correct answer)
- The vertical angle correction for curvature and refraction
- A type of prism used with total stations
- The calibration constant of a level rod
Correct answer: A method of measuring horizontal distances using crosshair intercepts on a rod
Stadia is an optical distance measurement method where the distance is computed from the intercept between upper and lower stadia hairs read on a leveling rod.
Question 5: When using a digital level, what is the function of the bar-code rod?
- It provides a magnetic north reference for the instrument
- It allows the instrument to electronically read rod height without a human reading (Correct answer)
- It measures atmospheric pressure for refraction corrections
- It stores benchmark elevation data in the field
Correct answer: It allows the instrument to electronically read rod height without a human reading
The bar-code pattern on a digital level rod is scanned by the instrument's CCD sensor, automatically computing the rod reading and distance without a manual observation.
Question 6: A retroreflective prism used with total stations returns light:
- At 90° to the incident beam regardless of angle of incidence
- Parallel to the incident beam back toward the source (Correct answer)
- Perpendicular to the prism face only
- At a fixed offset angle of 30°
Correct answer: Parallel to the incident beam back toward the source
A corner-cube retroreflector returns light parallel to the incoming beam back toward the source, making it ideal for EDM measurements over a wide range of angles.
Question 7: What is the purpose of applying an 'additive constant' (prism constant) correction in EDM measurements?
- To correct for atmospheric temperature changes
- To account for the offset between the prism's electrical center and its physical center (Correct answer)
- To compensate for Earth curvature in long distances
- To adjust for the instrument's horizontal circle eccentricity
Correct answer: To account for the offset between the prism's electrical center and its physical center
The prism constant corrects for the physical offset between the apparent reflection point of the prism and the true measurement point (the prism pole tip or target center).
RPLS Equipment and Tools Knowledge 2
What is the primary purpose of a tribatch (tribrach) on a surveying instrument?