# Zero Point

This chapter explains the Zero Point window, its prerequisites, differences between single-turn and multi-turn operation, saving, and verification after a power cycle. Calibration changes the position reference, so field safety conditions must be confirmed first.

## Before You Begin

Item | What to Check
--- | ---
Target device | The main window is connected to the target drive, and the current connection ID matches the field device.
Device state | The motor is stopped and disabled. Mechanical zero calibration must be performed while disabled.
Firmware version | This procedure is based on eTuner_V13.80. In actual use, prefer the latest released eTuner and firmware. Firmware information must be complete in Information, and the firmware must support this feature. Otherwise, the software reports that the current firmware does not support zero-point calibration.
Mechanical position | The user-defined mechanical-zero position, motion direction, travel boundaries, and limit states have been confirmed.
Safety measures | Confirm that the mechanism cannot collide, overtravel, or injure anyone and that stop, emergency-stop, or power-disconnection methods are available.
Save strategy | Save only after calibration is complete and the result is verified. Never save an unverified zero reference to the device.
Multi-turn battery | For a multi-turn model, connect the multi-turn battery before calibration and keep it connected during subsequent use. This does not apply to single-turn models.

High-risk operation: Mechanical zero calibration changes the current position reference. Do not perform long-travel, high-speed, or heavy-load motion immediately before or after calibration. Verify first at low speed over a short travel.

## Access and Interface

The Zero Point window guides you through Step1 to Step5 and shows position and position offset at the bottom.

The top of the window is arranged from Step1 to Step5. Follow the procedure below; this section only explains the entry point and easily misunderstood fields.

Entry/Area | Description | Notes
--- | --- | ---
Main Window → Zero Point | Opens the Zero Point window. | This entry appears in the client version. Connect the device and verify the firmware version before clicking it.
Reset Value | Sets the current position after reset in Step3. The single-turn value is fixed at 262144; enter the project-specified value for a multi-turn model. | Do not change 262144 for a single-turn model, and do not use the single-turn default for a multi-turn model.
Position | Shows the device's current feedback position. | After a power cycle, it must match the reset position set in Step3.
Offset of Position: | Shows the load-side position offset calculated by the last calibration. | This value is fixed after calibration and does not continually follow the current position. Do not save or move if it is abnormal.

## Procedure

1. Connect the target drive. Verify the current connection ID and firmware version in the main window, and make sure the motor is stopped and disabled.
2. Click Zero Point in the main window.
3. In Step1, click Motion and move the mechanism to the user-defined mechanical zero according to the field procedure. Skip this step if it is already at zero.
4. For a multi-turn version, confirm that the multi-turn battery is connected, click Reset Load Encoder in Step2, and wait for completion. Skip this step for a single-turn version.
5. In Step3, verify the reset position: keep 262144 for a single-turn model or enter the project-specified value for a multi-turn model. Click Reset once only.
6. After clicking Reset, wait about one second for the position-reset-command-success message, then verify position and position offset.
7. Click Save in Step4, wait about three seconds, and confirm success. Do not power off or perform another operation while saving.
8. Power-cycle and reconnect the device according to the field procedure.
9. Open Status Monitor and confirm that the current position equals the Step3 reset value.

After replacing or reinstalling a module, recheck mechanical zero and repeat this calibration. If the current position does not equal the reset value after a power cycle, or the position offset is abnormal, do not run absolute-position motion. Stop, record the current position, offset, and messages, and contact a ZeroErr engineer.

## Single-Turn and Multi-Turn Differences

Version | Step2 | Step3 | Verification
--- | --- | --- | ---
Single-turn version | - | The reset position is fixed at 262144. Position offset = 262144 - current position before reset. | After a power cycle, confirm that Status Monitor shows position 262144 and that feedback remains within 0-524287 over the operating range.
Multi-turn version | Connect the multi-turn battery, then run Reset Load Encoder and wait for completion. | Enter the project-specified reset position. Position offset = reset position - current position before reset. | Keep the multi-turn battery connected. After a power cycle, confirm that Status Monitor shows the reset position and that the offset matches project expectations.

“Current position before reset” means the load-encoder position shown in Status Monitor. After reset: current position = reset position = load-encoder position + position offset. Current position changes with feedback; the offset remains the result of the last calibration.

A single-turn model resets mechanical zero to the midpoint 262144, leaving maximum range in both directions. Feedback must remain within 0-524287 during operation, or zero may be lost after a power cycle.

## Troubleshooting

Symptom | Recommended Action
--- | ---
Firmware information is missing after opening the feature | Confirm that the device is connected and the firmware version has been read in the main window. If still missing, contact engineering or technical support.
Current firmware does not support mechanical zero calibration | Do not continue. Upgrade according to the project process or contact support.
No success message after clicking Reset | Do not click Reset again; a repeated reset recalculates the offset from a new current position. Check connection, errors, and Status Monitor. Reconnect and restart the procedure if necessary.
Multi-turn position is lost after a power cycle | Stop further motion. Check that the multi-turn battery was connected before calibration and remained connected, record the field state, and contact a ZeroErr engineer.
Position does not equal the reset value after saving and power-cycling | Stop further motion. Record position, position offset, firmware version, and steps performed, then contact a ZeroErr engineer.

For the latest firmware and upgrade instructions, see the eRob firmware upgrade page.