Web Exclusive! Insight into Instrument Repair

August 19, 2002
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Items, techniques, time frames, expertise.

When you’re the one measuring the world, instrument repair is inevitable as it is for every surveyor. Since surveyors are so dependent on their instruments, the efficiency and quality of the repair process must meet high standards. Specifics including timing, cost and reliability of the repair person carry a heavy weight. Surveyors often find themselves trying to fix problems themselves. But since 43 percent of the respondents of a POB Online Point of View poll taken in May indicated that they don’t know how to repair their instruments, it is imperative to know of a reliable instrument repair shop. Once you get the equipment there, you, like any other consumer, want satisfactory service and turnaround. Is this the general experience?

When It’s Time to Take It In

More than 50 percent of POB Online Point of View respondents (138 total) said they have their instruments repaired only when needed. A small four percent head out to the repair shop regularly every six months, and 37 percent have them repaired annually.

“Sending instruments in for repair or calibration on a regular basis provides a basis for knowing your crews have the right tools to do their job,” says Ernest Warner, a professional land surveyor in private practice. “How often do you have your car serviced? Probably no one will sue you if your car breaks down, but if you stake infrastructure in error due to your instrument being out of calibration, watch out.”

Some surveyors are more comfortable sending their conventional units back to the factory instead of looking to repair shops. However, factory-backed repairs are often not as convenient since some factories are states away from the surveyor in need. The bottom line is that instruments need minor fixes and repairs all the time if you want to stay productive.

“With modern instruments becoming more electronic and less mechanical it is getting increasingly difficult to do calibration or repair work onsite. All of our equipment is fully robotic. We’re fortunate enough to have an extra unit so rotating equipment for service needs doesn’t interrupt our production. I consider the extra expense for service of robotic equipment is offset by the added production rates gained by their use,” says Tony Ware, a survey manager in Dallas, Texas.

Satisfaction Guaranteed?

Sure, you may be able to “fix” your own instrument on occasion, which is great during an in-field emergency, but do you know all the ins and outs of complete instrument repair? Will you seal the equipment to protect it from water and dust, for instance?

“I have a True Plumb pole adjustment outfit from Chrisnik [Inc., Ross, Ohio] and an Optical Plummet Tribrach Adjustment outfit, both purchased from LO Ink [Specialties, Kennebunkport, Maine],” says Sam Clemons, LS, owner of Clemons Surveying in Jasper, Tenn. “We can run some checks and adjustments on our total station, but if we even think it is messed up or needs adjustment (usually some kind of blow or drop knocks it out), we take it to Hayes Instruments for adjustment.”

Hayes Instrument of Shelbyville, Tenn., a 30-year-old firm regarded highly by surveyors, sees a lot of instruments in its daily routine. Total stations are the instruments fixed the most at Hayes for two reasons: they are the instruments most sold and most used. John Boyd, president of Boyd Instrument & Supply Co. Inc., of Horsham, Pa., experiences the same when it comes to the most frequent repairs.

“For contractors, it’s levels; for surveyors it’s total stations,” Boyd says. “Mainly because surveyors aren’t using levels as much, so the more you use a total station, the more fixing it needs.”

There aren’t any instruments surveyors can fix themselves, according to Hayes President/Owner Eddie Clanton. Minor adjustments can be done, he says, such as adjusting the optical plummet or the level vial, or checking the EDM on a baseline.

“Ninety-nine percent of the time they’ll have to bring it in,” Clanton says.

Boyd agrees that no instruments can be fully repaired by the average surveyor. Basic, simple onsite calibrations and checks can be done onsite, though, Boyd says. His shop now carries a patent-pending prism pole adjustment tool. Coined as the “Prism Pole Field Adjuster,” it can be used conveniently onsite.

“There’s no reason to drive for an hour for something like that when you can fix it in the field,” Boyd says. Boyd’s father, an instrument maker since 1945, designed the tool, which sells for $39.95. Boyd says his office had presold quite a few before the tool was even manufactured.

Only four percent of our poll respondents know how to repair their instruments on their own. Fifty-three (53) percent do know how to repair at least some of their instruments. But if you’re in that “99 percent of the time” category and you don’t know how to fix your instrument, a qualified technician is required. Almost 60 percent said that the technicians at their repair shops were qualified to perform the work.

Service Satisfaction

When you are in need of repairing your instrument quickly because the project completion date is rapidly approaching, nothing matters more than quick turnaround.

When surveyors find themselves lugging their equipment to Hayes, they can expect to pick it up in two to three days for simple maintenance and calibrations, and 10 days minimum for repairs, Clanton says. Boyd Instrument & Supply Co. promises a 10 working day turnaround as well.

Our recent poll indicated that surveyors usually experience a fast turnaround time. Usually. But, what about the times when the repair has no promise of quick turnaround? What about the times when the parts have to be ordered, and they won’t be in soon enough? Do you get a loaner, borrow from a nearby firm, buy another unit for the interim? Fifteen (15) percent said that the shops they used provided loaners, 45 percent said they provided both loaners and rentals and 26 percent said they provided rentals only. The remaining 15 percent said they provided neither.

If you are given a loaner or rental, test it first or get one that is equivalent to the one you’re having repaired. Have the instrument checked and calibrated before you walk out the door.

Should Hayes need to keep instruments longer than its 10-day minimum, customers are offered loaners or rentals. “[We offer] both,” Clanton says. “It depends on the situation. If they are new customers, we’ll probably offer them rentals. Regular customers who can be trusted can take rentals.” Clanton also said all rentals are calibrated and checked before being handed over.

John Boyd of Boyd Instrument & Supply Co. Inc., says many more loaners are provided to customers than rentals, especially since some small surveying firms may be turning in their only total station for repair. Boyd provides them with a loaner compatible to the one turned in for repair, completely calibrated and checked. Rentals run from $200 to $500.

Hayes provides a 120-day warranty on parts and workmanship unless the equipment is mishandled, which is defined as equipment that has been dropped or misused.

Instruments Most Repaired and Why

Some common instrument problems:
John Boyd of Boyd Instruments & Supply Co. Inc., highlights three main instruments and easy “fixes” in a seminar called Surveying Equipment Adjustments he has given at state society conferences: prism poles, automatic levels and total stations.

Broken down, some of the common problems and fixes are:

  • Prism poles
    Common problem: level vial out of adjustment
    Causes: Adjustment is out; worn or striped threads in vial housing and/or screw; worn or missing rocker; housing is loose; vial is defective
    Trouble-shooting: Make sure the housing is tight on the pole. Make sure that vial is not loose is the housing. Press on the dot with a dull pencil; the bubble should not move.
    Calibration procedure:
  • 1. Make a mark on the top of a door jam
  • 2. Transfer the mark onto the floor using a plumb bob
  • 3. Place an extra point on the top thread of the pole
  • 4. Place the bottom point of the pole on the mark on the floor
  • 5. Extend the pole until the top point is on the mark on top
  • 6. The bubble should be centered in the circle of the vial
  • 7. If it is not in the center, adjust in using three screws
  • 8. Rotate the pole 180 degrees. The bubble should still be in the center. If not, readjust taking out ½ the error.

    Automatic Levels
    Common problem: circular level vial is off
    Causes: The vial is out of adjustment, the tension of leveling screws is too tight, the center is loose, the vial is loose in housing or the vial is defective.
    Calibration procedure:
  • 1. Set the instrument up on a tripod and carefully center the bubble of the circular level vial using three leveling screws.
  • 2. Revolve the telescope 180 degrees around vertical axis. If the bubble remains centered, no adjustment is required.
  • 3. If the bubble is not centered, loosen the adjustment screw opposite the bubble slightly, then tighten the adjustment screw nearest the bubble. Take out only ½ the error.
  • 4. Re-center the circular vial level bubble using the three leveling screws.
  • 5. Go back to step 2. If bubble remains centered you are done. If bubble is not centered, repeat steps 3 to 5.

    Automatic Levels
    Common problem: The level line is off.
    Causes: The cross wires are out of adjustment, there is a loose objective lens, the compensator is sticking.
    Collimation procedure:
  • 1. Set up the instrument on a tripod at a point midway between two walls or two hubs, which are about 150 feet apart.
  • 2. Level the instrument using the three leveling screws.
  • 3. Place identical scales against both walls and collimate both scales on a horizontal line of sight, using the same number on both scales if possible.
  • 4. Set up the instrument about 6 to 10 feet from Target “B.”
  • 5. Sight Target “A” and record reading (Call A1).
  • 6. Sight Target “B” and record reading (Call B1).
  • 7. Set up the instrument about 6 to 10 feet from Target “A.”
  • 8. Sight Target “B” and record reading (Call B2).
  • 9. Sight Target “A” and record reading (Call A2).
  • 10. If the difference from (A1 to B1) = (B2-A2) no collimation is required. If the difference is out of the manufacturer’s specifications then collimation must be performed.
  • 11. Sight the farther scale and move the horizontal crosshair line up or down as required until the line coincides to the same reading as that of the nearer scale.
  • 12. First loosen the adjustment screw on the side to which the horizontal crosshair line has shifted. Then tighten the adjustment screw on the opposite side.

    Total Stations
    Common problem: The level vial is out of adjustment.
    Causes: The level vials are out of adjustment, are loose in housing, are defective, the center is bent or loose, or there is too tight of tension of leveling screws. Plate level vial:
  • 1. Align the plate vial parallel with two of the leveling screws. Then center the bubble using the two leveling screws.
  • 2. Rotate the plate vial 90 degrees around the vertical axis. Center the bubble using the one remaining leveling screw.
  • 3. Rotate the plate vial 180 degrees around the vertical axis.
  • 4. No adjustment is required if bubble remains in the center.
  • 5. If the bubble is not centered, move it ½ way back using the leveling screw that is parallel to the plate vial.
  • 6. Move the bubble the remaining ½ using the bubble adjusting nut.
  • 7. Rotate the plate vial 180 degrees around the vertical axis, and check if the bubble stays in the center. If the bubble is not centered, repeat the procedure.

    Total Stations
    Common problem: The optical plummet is out of adjustment.
    Causes: Out of adjustment, housing is loose.
    Optical Plummet:
  • 1. Set the instrument on a tripod and place a piece of white paper with an “X” drawn on it immediately under the instrument.
  • 2. Look through the optical plummet and move the paper so that the intersecting point of the cross comes to the center of the optical plummet crosshair or dot. Get as close as possible.
  • 3. Adjust the leveling screws so that the center mark of the optical plummet coincides with the intersection point of the “X.”
  • 4. Rotate the instrument 180 degrees around the vertical axis.
  • 5. Look through the optical plummet to see if the center mark still coincides with the “X.” If it does not, adjustment is required.
  • 6. If the marks do not coincide, use the leveling screws to adjust ½ the error and the optical plummet adjusting screws to adjust the remaining error.
  • 7. Rotate the instrument 180 degrees around the vertical axis.
  • 8. Look to see if the marks coincide. If they do, no further adjustment is required. If they do not, repeat the procedure.

    Total Stations
    Common problem: Collimation is out of adjustment.
    Causes: The wires are out of adjustment.
    Collimation procedure:

  • 1. Set the instrument on a tripod, level the instrument and turn on the instrument.
  • 2. Set the vertical angle to 90 degrees and sight a target about 100 to 150 feet away.
  • 3. Zero set the vertical angle.
  • 4. Rotate the instrument to sight the same target in the F2 position.
  • 5. Read the angles. Vertical should be 270 degrees and horizontal should be 180 degrees. Readings should be within manufacturers specifications.
  • 6. If the error is greater than specified, adjustment is required. Take ½ the error out using the tangent screws and ½ out using the crosshair adjusting screws.
  • 7. Repeat if required.

    Zero set procedure:

  • 1. Set the instrument on a tripod and set a prism in a tribrach about 6 feet from instrument. The heights should be as close to equal as possible.
  • 2. Turn the instrument on using the factory mode as described by the manufacturer.
  • 3. Sight on the prism in F1 mode.
  • 4. Enter reading.
  • 5. Sight on prism in F2 mode.
  • 6. Enter reading.
  • 7. The instrument will compare the first and second reading and zero them out.


    Total Stations
    Common Problem: Distance measurements are not possible, weak, incorrect, or not to maximum specifications.
    Causes: The prism constant is wrong, instrument constant is wrong, EDM beam is out of alignment, LED is defective or weak, optical fiber is broken.

    Instrument Constant
    Normally, the instrument constant does not have any discrepancy. However, it is recommended when measuring the instrument constant to compare it with an accurately measured distance at a place where the precision is specifically indicated once every six months.

  • 1. Provide a Point “C” on a straight line, between Points “A” and “B.” Make sure that Point “C” is not at an even foot reading. Line “AB” should be almost horizontal and about 300 feet long. Set the instrument on Point “A” and measure line “AB” and Line “AC.” Then set the instrument on Point “B” and measure Line “BC.” Repeat this procedure several times.
  • 2. If the difference is 5 mm (or the tolerance of the instrument), the instrument constant may need to be adjusted.

    Alignment of EDM and optical axis
  • 1. Position the instrument on a tripod and set a prism in a tribrach about 6 feet from the instrument. Make sure the prism is facing straight back toward the instrument.
  • 2. Power up the instrument.
  • 3. Set crosshairs on center of prism. (It is better to use a target on the prism.)
  • 4. Set the instrument on the continuous measurement mode.
  • 5. Look through the eyepiece and take the telescope out of focus until the red dot is displayed (will not work on all instruments).
  • 6. If the displacement of the red dot is within 1/5 of the diameter of the red dot in reference to the crosshairs, no adjustment is required.
  • 7. If displacement is more than 1/5, contact your dealer.

    So if you need your instrument calibrated, consider a "quick-fix" in the field. But if the repair is beyond your knowledge, trust it to the experts.

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