CALIBRATION FOR LAL20X & LAL24X

Transcription

1 CALIBRATION AND FAULT FINDING FOR LAL20X & LAL24X DUMPY LEVELS MEASURING EXPERTS SINCE 1869

2 How The LAL20X & LAL24X Works The Automatic level is called Automatic because it requires only a simple basic set-up using the external circular leveling vial. The final fine adjustment is then made by an internal pendulum mechanism called the compensator. This enables a very accurate set-up to be performed by personnel with only basic training in the use of surveying instruments. The compensator is quite delicate and is protected from damage by a compensator lock that is activated by closing the lid of the travel case. It can also be manually activated by squeezing the button below the eyepiece. Compensator

3 Setting up a Dumpy Level Place the Dumpy Level on a tripod or other solid stable surface. Adjust the three black leveling screws until the bubble in the circular vial is within the black circle. This vial can be viewed through the prism on the left hand side of the Level if required. Note; The bubble does not have to be exactly in the center of the circle. Turn the level in the direction required using the alignment sight on the top of the level as a guide. Look through the eyepiece and adjust the focus of the cross hairs by turning the eyepiece. Then adjust the focus of the target using the Focusing knob on the right hand side of the level. The horizontal cross hair now shows a line that is exactly level with the Dumpy. Pi Prism Alignment Sight Circular setting Vial Focus Knob Leveling screws Eyepiece

4 Common faults The most common fault is the circular or setting vial being out of alignment. Further on we will discuss how this can be checked and re-aligned. Not focusing correctly is mostly caused by the focus travel being adjusted incorrectly. Compensator accuracy can only be properly checked over a suitable range. We can however easily check that the compensator is functioning. Physical damage, usually from being dropped is common and often requires replacement of the compensator and sometimes the whole unit has to be exchanged.

5 Circular Setting vial To check the operation of the circular leveling vial. Firstly we place the Dumpy on a solid stable surface. We then adjusting the three black leveling screws while viewing the bubble through the prism on the left hand side of the Level, until the bubble in the circular vial is close to the center of the black circle.

6 Circular Setting vial Now rotate the level 180 degrees while holding the base firmly. If the circular vial is set up correctly, the bubble will remain within the circle. Note; Some customers believe that the bubble must remain precisely in the center of the circle, but this is not correct. The bubble only has to remain within the circle. If the bubble remains inside the circle then no adjustment is required.

7 Removing the Orange Cover If you the circular vial requires adjustment then it is best if the orange cover is removed so it is easier to see the circular vial. Unscrew the Eyepiece Ring. Using two slim straight bladed screwdrivers, insert the ends under the cover as shown below. This will release the front of the cover. The cover should lift at the large lens end allowing you to gently pull the top off. Eyepiece Ring Screwdriver Tip here Screwdriver Tip here Eyepiece

8 Circular Setting vial Adjustment Place the Dumpy level e on a firm solid surface so that the Objective e (big end) is on the left and the Eyepiece is on the right. Adjust the three Black leveling screws until the bubble is as close to the center of the circle as you can.

9 Circular Setting vial Adjustment Holding the base of the level so that it does not move at all, rotate the top part of the level by 180 degrees (Half a turn). We now adjust the two silver Hex screws to correct the bubble position using a 2.0mm Hex driver or key. Note that when you turn the screw clockwise (tighten) you will move the bubble towards the screw and when you turn the screw counterclockwise you will move the bubble away from the screw. See arrows below.

10 Circular Setting vial Adjustment It is important to note that you are not trying to move the bubble to the center point of the circle using the silver hex screws. In fact you are trying to move the bubble only half the distance required as the effect is doubled, so be careful to make only small adjustments, no more than half a turn.

11 Circular Setting vial Adjustment Holding the base of the level so that it does not move at all, rotate the top part level by 180 degrees (Half a turn) back to the original position with the Objective (big end) on the left and the Eyepiece on the right. Again we adjust the Black leveling screws until the bubble is as close to the center of the circle possible. We now repeat the process adjusting the three black leveling screws while the eyepiece is on the right and adjusting the two silver hex screws while the eyepiece is on the left until the bubble remains inside the circle in both positions. It is quite normal to repeat this several times to get a good result. Adjust Black Screws Adjust Silver Screws

12 Problems with vial Adjustment Problems that you may find are as follows; o The hex in the silver screw is stripped and the driver slips. In this case the screw should be replaced. If you cannot remove the screw then it is a workshop job. The screw is turning but the bubble is not moving or the screw is so tight that it will not turn. These both mean that the screw has run out of adjustment. The problem can be addressed by tightening the spring under the circular vial or adjusting the third mounting screw but that is usually a job for the workshop. The bubble will not settle in the center of the circle. This is a fault with the vial itself and usually means that t vial must be replaced.

13 Adjusting the Focus travel If the Dumpy will cannot be focused then;- Firstly check that the slide is moving inside the tube. The slide can be seen through the objective (big) lens and should move when the focus knob is turned. If the slide does not move then it is a workshop job. If the slide does move then the focus travel limit will be stopping the slide too soon. This can be fixed as follows;- Remove the top cover as described previously. Focus clamp Undo the two Focus clamp screws by about 1 turn only. screws While looking through the eyepiece, turn the focusing knob clockwise until it an object at least 20m away comes into focus. The knob will feel gritty but this is normal. Continue turning the knob for a quarter of a turn past the point of focus. Retighten the two clamping screws.

14 Testing the Compensator operation If there e is any doubt that the Compensator is functioning correctly then is can be tested as follows. Set up the dumpy level on a firm stable surface and adjust the three black leveling screws so that the bubble in the circular vial is within the black circle. Look through the eyepiece and make sure that the cross hairs are clearly in focus and adjust if required by turning the eyepiece. Look through the eyepiece and focus the level using the knob on the right hand side, on any object that t can be seen clearly. l While looking through the level turn the black leveling screw nearest to you by approximately a quarter of a turn. If the compensator is functioning correctly then the cross hair will move either up or down and then return to the original position. This is the compensator, correcting for the error as the screw was moved. If the line moves and does not recover then the compensator is not functioning and this is a job for the workshop.

15 Reassembly Screw the Eyepiece Ring onto the level by placing it over the end of the level and turning anticlockwise until the thread engages with a small click, then turn clockwise for approximately 2 turns. Place the orange cover onto the level noting the piece that fits between the Eyepiece Ring and the body and then press the cover firmly downwards. It should clip into place. Note this may require some force. Complete tightening the Eyepiece Ring by turning clockwise. Note; it is quite difficult to fit the Eyepiece Ring if the cover has already been installed. Replace the lens cover, place the level in the travel case and close the lid firmly to lock the compensator. Eyepiece Ring