Pajari Instruments Ltd., since 1945




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   Tropari - Checking for Accuracy and Working Conditions

The tests outlined below will allow a user to efficiently determine the working condition of a Tropari Borehole Surveying Instrument. If the instrument passes all of the sensitivity tests, then the accuracy of readings will be within one degree of azimuth and inclination.

  Sensitivity Tests

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1. Place the instrument on end (vertically) on a table and rotate the inner frame. As most tables are not perfectly horizontal,   note whether the inner frame turns freely to seek the slope of the table.  If the inner frame stops turning without seeking the slope, or stops turning with obvious frictional retardation, then the lowermost end pivot/jeweled bearing is injured.  Turn the instrument 180 degrees and repeat test on the end  pivot/jeweled bearing.

2. Place the instrument on a horizontal surface near (and facing) the edge so that the inclination markings and the protractor pin can be viewed simultaneously with a magnifying glass (see Figure 1). If the instrument is placed on a table, it will be necessary to kneel on the floor to observe this test.

Figure #1
View of instrument required
for sensitivity test #2.
(Click on Figure #1 to enlarge)


Hold onto the end of the outer frame so that the instrument does not roll off the edge.

With a finger, set the unlocked gimbal oscillating and note the readings when the gimbal comes to rest. Repeat and note reading. If the two readings are with degree of each other, the sensitivity and accuracy of the inclination readings are within factory specifications and the side pivot/jeweled bearings are perfect. If the two readings are 1 degree different, the inclination will still be more accurate than acid tests. Greater differences indicate a need for servicing.

3. Place the instrument on a horizontal surface and view the compass plate from the top. Attract the compass with a piece of iron (paper clip, pen knife etc.) so that the compass oscillates freely seeking magnetic north, and if it repeatedly (2 or ore tests) comes to rest within 1 degree of azimuth, the compass pivot/jeweled bearings are perfect.

These tests can be accomplished in 5-10 minutes. Since accuracy in the Pajari instrument is only dependent on its sensitivity, these tests effectively determine accuracy.

  Timing Accuracy

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1. When the instrument is fully locked turn the timing ring gently toward the timing readings (to the left). There must be a small amount of free (effortless) rotation of the timing ring before it engages the internal levers. Note where the setting mark on the timing ring (see Figure 2) comes to rest when resistance is encountered. If the setting mark is coincident (+ or - 1 minutes) with the first or zero timing mark, then normal operating procedures are valid.


2. Turn the timing ring so that exactly 10 minutes of timing has been activated. At this time setting the compass plate and gimbal should be free.


3.  Set exactly one hour of time on the instrument and note the time on a watch. Start the instrument by oscillating it (see Figure 3) and make sure the timing ring has been returned to the extreme right-hand position. After 50 minutes by the watch, gently rotate the timing ring to the left until resistance is encountered. If the mechanism is running time-true, the setting mark will indicate 10 minutes of time remaining, If the mechanism is running slow there will be more than 10 minutes of time remaining. If fast, less than 10 minutes.


Figure #2

Terminology for Timing Tests.

(Click on Figure #2 to enlarge)

Starting the Tropari

Figure #3

Correct procedure for starting instrument.


The results of these tests will indicate whether the instrument is running time-true. Timing errors do not affect the accuracy of the instrument other than the possibility that the instrument may begin to lock on lowering or not be securely locked during retrieval from the test depth. Corrections can be applied to the setting time if the instrument does not run time-true as follows:

  • If the setting mark is not at zero when the instrument is locked with + or minus 1 minutes (Test 1), add or subtract time required for a specific time setting (add time if setting mark is past zero). If there is not free movement of the timing ring before resistance is encountered when the instrument is locked, the locked instrument may not be secure and jarring may cause the readings to move. This problem has to be rectified.

  • If the gimbal and compass do not rotate freely when 10 minutes of running time is set, determine at what time setting these are free. This would not be more than 1 or 2 minutes past 10 minutes (11 or 12 minute time setting) if the instrument is otherwise functional. To correct, simply allow 11 or 12 minutes for the instrument at its survey position.

  • If the instrument runs fast, say 3 minutes, then when one hour of lowering time is required, set the instrument at l hour, 15 minutes (1 hour lowering plus 10 minutes at rest plus 5 minutes error in running time). A 30-minute lowering requirement would require one-half of 5 minutes or a 2- minute in running time correction.


Subtract correction if tests indicate instrument runs slow.

Although the details of these timing tests may appear complex, the corrections conveyed to the user would consist of a statement such as, for example: Allow an additional ----- minutes for lowering and locking time.

This simple statement would include all corrections and would seldom amount to more than 5 or 6 minutes, but still necessary so that the instrument will have definitely locked at rest during a test. For those surveyors that reach the test depth well in advance of the last 10 minutes and wait for 5-10 minutes after time is up, these corrections are not necessary.


Pajari Instruments Ltd. 2015

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