Rotary Drilling Rig One-Direction Depth Signal Diagnosis

A rotary drilling rig can continue to move even when its depth indication is wrong, but that does not make the fault minor. Depth information helps the operator follow the drilling plan, compare progress between passes, and document completed work. In this field case, the displayed value increased in the negative direction but would not increase in the positive direction.

The symptom could have come from the two proximity switches, their wiring, the controller inputs, or the display. The technicians used comparison tests, temporary signal connections, controller substitution, and voltage measurements to identify which parts could respond correctly.

This article is based only on the supplied service report. It retains the recorded terminals, measured values, test sequence, and repair result while removing technician names and internal organization details. The measurements describe this machine at the time of diagnosis and are not universal specifications for every rig.

The Depth Value Changed in Only One Direction

The operator reported that the depth display showed negative accumulation but no positive accumulation. Because the display was not completely blank, the fault did not immediately prove that the screen or controller had failed. One signal state was still reaching or being interpreted by the system.

The report listed four possibilities: a failed proximity switch, wiring fault, controller problem, or display problem. This covered the path from sensing point to operator display.

Observed symptom: the depth reading increased in the negative direction only.
Sensor stage: two proximity switches generated the directional pulse states.
Signal stage: wiring carried the two signals to controller inputs XM3.18 and XM3.19.
Display stage: the controller and monitor converted the input sequence into a depth value.

Separate the Sensors, Wiring, Controller, and Display

Two new proximity switches were installed, but the symptom remained. The new and existing switches were then tested on a neighboring rig, where the depth display responded normally. That comparison showed that simply fitting new sensors to the affected machine was not enough and that the switches themselves could operate.

The team next bypassed the original route with temporary signal wires connected to XM3.18 and XM3.19. This early bypass did not change the symptom, so the investigation continued rather than treating the first wiring test as final proof. The affected machine's controller was then installed on the neighboring rig, where the depth display operated normally. That substitution reduced the likelihood of an internal controller failure.

To check the downstream input and display path, the lower-carriage swing encoder outputs were connected to XM3.18 and XM3.19. Rotating the upper structure produced a normal depth response on the display. The controller inputs and display could therefore recognize a valid alternating signal.

A replacement part that does not change the symptom is a test result, not a completed repair.
Testing the same sensors on another rig helped separate sensor condition from machine wiring.
Moving the controller to a working comparison machine checked whether it could process depth signals.
Feeding a known encoder signal into the depth inputs checked the controller-to-display path.

Temporary signal connections at the rotary drilling rig controller

Voltage Measurements Documented the Switching States

The report photographs record the switch outputs while the indicator states changed. One active-state reading was approximately 22.3 V to ground, and another active-state reading was approximately 23.0 V. In the inactive state, the recorded output was approximately 1.3 V. The probe supply photograph showed approximately 23.8 V between the 24 V supply and ground.

These values mattered because the team was not relying only on whether an indicator lamp appeared bright. The meter documented that the switches produced distinct high and low states. Combined with the comparison-rig tests, the evidence pointed away from a simple two-sensor failure and back toward the identity and continuity of the signal conductors on the affected machine.

Recorded active output at L1: approximately 22.3 V to ground.
Recorded active output at L2: approximately 23.0 V to ground.
Recorded inactive output: approximately 1.3 V to ground.
Recorded probe supply: approximately 23.8 V between supply and ground.

Multimeter measurement of a proximity-switch output state

Wire Identification and Complete Signal Runs Led to the Repair

After the sensors, controller, and display path responded correctly in comparison tests, the remaining focus was the signal wiring and wire identification. The report records that the team reconsidered the wire numbers. Replacing the signal wires from the proximity switches to the controller completed the repair.

After replacing those complete signal runs, the depth display returned to normal operation. The result confirmed a case-specific fault in the sensor-to-controller signal path. It also explains why the diagnosis required more than installing new proximity switches: the sensors could switch, but the machine still needed the correct signals to arrive at the correct controller inputs.

Confirmed repair area: the proximity-switch signal wiring to the controller.
Corrective action: verify wire identification and replace the complete signal conductors.
Verification: positive and negative depth response returned to normal.
Final result: normal depth display was restored without replacing the controller or display.

What a Used-Rig Buyer Should Ask to See

A used-rig inspection should demonstrate more than a changing number on the screen. Ask for continuous video showing the depth value responding through both directions of the sensing sequence. The video should include the sensor area, display, and a short operating cycle so that a frozen or one-direction value is visible.

Where a previous repair is reported, request photographs of the final harness routing, connector support, insulation, and wire identification. Temporary external wires can be useful during diagnosis, but export preparation should end with protected, mechanically supported wiring suitable for vibration, dust, and repeated mast movement.

The best evidence is a connected chain: a repeatable symptom, measurements at named points, a repair that addresses the isolated section, and a final test performed under the same conditions. This is the standard Kepler Machinery applies when presenting technical condition to overseas buyers.

Confirm the depth value responds in both directions, not merely that the display is powered.
Ask whether sensors were tested individually and whether their high and low states were measured.
Inspect repaired wiring for correct routing, strain relief, sealing, and identification.
Keep the before-and-after test record with the machine's inspection documentation.

Follow the Complete Signal Chain

This case was resolved by treating the depth system as a complete signal chain. Comparison-machine tests showed that the proximity switches and controller could operate, a known encoder signal proved the display path, and voltage measurements documented distinct switching states. The final wire-number review and replacement of the complete signal runs restored normal depth display.

For an overseas buyer, that diagnostic record is more valuable than a simple statement that the screen now works. It shows which components were tested, what evidence ruled them out, where the repair was made, and how the result was verified.

Safety Note

Electrical tests on a rotary drilling rig must be performed by qualified technicians using the correct wiring diagram, insulated probes, secure machine isolation, and safe access around moving components. Do not bridge controller inputs or substitute encoder signals unless the circuit design and voltage levels have been confirmed.