Chapter 3. Sensor Control

The sensor can be controlled via a computer using the scream software or by using the 4 push button switches on the lid. The instrument control functions are performed by the SoH. The functions available by push button on the lid are: Unlock, Centre, and Lock. Two busy LEDs indicate the instrument's status, one red and one green. The sensor has an automatic lock feature that can be enabled to ensures that the sensor is always locked when transported. It also has an automatic centre function that can be enabled to centre the instrument if the mass position exceeds a set threshold.

3.1 Unlock

To initiate the unlock function, hold down the unlock button, then press the enable button and release both after approximately 10 seconds. The SoH will now perform the task of unlocking the sensor. There are several stages to this and the green busy LED indicates the progress. If, during the unlock process, an error is encountered the red busy LED will illuminate at the end of the operation, indicating the fault encountered. Details of LED states can be found in section 3.6.

3.2 Centre

To initiate the centre function, hold down the centre button, then press the enable button and release both after approximately 10 seconds. The SoH will now perform the task of centring the sensor. The green busy LED flashes during the centre process and then stays on once the centring is successful. If, during the centre process, an error is encountered, the red busy LED will illuminate at the end of the operation, indicating the fault type encountered. Details of LED states can be found in section 3.6.

3.3 Lock

To initiate the lock function, hold down the lock button, then press the enable button and release both after approximately 10 seconds. The SoH will now perform the task of locking the sensor. There are several stages to this and the green busy LED indicates the progress. If, during the lock process, an error is encountered, the red busy LED will illuminate at the end of the operation, indicating the fault encountered. Details of LED states can be found in section 3.6.

3.4 Auto-lock

To enable and disable the auto-lock function, hold down both the centre and the unlock button down, then press the enable button until the red LED illuminates continuously (around thirty seconds). This toggles the auto-lock function on and off; i.e. do this once to enable and then again to disable. Both busy LEDs blink together continuously to indicated the sensor's mode. The sensor should not be in a fault state prior to enabling this function. Details of LED states can be found in section 3.6.

When Auto-lock is enabled, the sensor will use its internal battery to lock the sensor approximately thirty seconds after the power has failed.

Caution: If the sensor has been left standing powered off for extended periods of time (more than three months), the sensor should be powered up and then left for at least forty-eight hours before deployment to ensure that the internal battery is charged. Failure to do this may result in the auto-lock function failing and consequential damage to the sensor if it is moved while unlocked.

The period of time between power failure and sensor auto-locking can be set by the user but direct access to the sensor is necessary. In the case of digital sensors, it will require the removal of the digitizer lid: refer to section 5 for additional details.

3.5 Auto-centre

To enable and disable the auto-centre function, hold down both the centre and lock buttons down, then press the enable button until the red LED illuminates continuously. Do this once to enable, then again to disable: both busy LEDs blink together continuously to indicated the sensor's mode. The sensor should not be in a fault state prior to enabling this function. Details of LED states can be found in section 3.6.

When auto-centring is enabled, the sensor will initiate a centring operation if the mass position of any component continuously exceeds the threshold for a set delay period.

The default threshold is set to ±1000 counts which is ±50% full scale. The delay period is set to 10 which equates to around 10 minutes.

Note: These “counts” refer to the output of an internal, dedicated analogue-to-digital converter. They are proportional to, but not equal to, the mass position outputs of the main digitiser.

The auto-centre parameters can be set by the user but direct access to the sensor is necessary. In the case of digital sensors it will require the removal of the digitizer lid. Refer to section 5 for additional details.

3.6 Busy LEDs

The busy LEDs indicate the current status of the instrument by flashing in different sequences. The sequences are based on eight time segments, repeated continuously. Each LED can be on or off during each time segment.

The symbol ○ indicates that the led is off during a time segment and the symbol ● (or ●) indicates that the red (or green) LED is on. For example, the sequence of symbols ○○○○○●○● indicates that the green LED is off for a long period of time (5 segments) then flashes twice.

LED sequence	Description of status
Red: ○ ○ ○ ○ ○ ○ ○ ○ Green: ○ ○ ○ ○ ○ ○ ○ ○	Sensor is locked or powered off and no automatic functions are selected.
Red: ○ ○ ○ ○ ○ ○ ○ ● Green: ○ ○ ○ ○ ○ ○ ○ ●	Only auto-centre is enabled.
Red: ○ ○ ○ ○ ○ ● ○ ● Green: ○ ○ ○ ○ ○ ● ○ ●	Only auto-lock is enabled.
Red: ○ ○ ○ ● ○ ● ○ ● Green: ○ ○ ○ ● ○ ● ○ ●	Both auto-lock and auto-centre are enabled.
Red: ○ ○ ○ ○ ○ ○ ○ ○ Green: ● ● ● ● ● ● ● ●	Sensor is centred: auto-lock and auto-centre are both disabled.
Red: ○ ○ ○ ○ ○ ○ ○ ● Green: ● ● ● ● ● ● ● ●	Sensor is centred and only auto-centre is enabled.
Red: ○ ○ ○ ○ ○ ● ○ ● Green: ● ● ● ● ● ● ● ●	Sensor is centred and only auto-lock is enabled.
Red: ○ ○ ○ ● ○ ● ○ ● Green: ● ● ● ● ● ● ● ●	Sensor is centred and both auto-lock and auto-centre are enabled.
Red: ○ ○ ○ ○ ○ ○ ○ ○ Green: ○ ○ ○ ○ ○ ○ ○ ●	Sensor is locking.
Red: ○ ○ ○ ○ ○ ○ ○ ○ Green: ○ ○ ○ ○ ○ ● ○ ●	Sensor is unlocking
Red: ○ ○ ○ ○ ○ ○ ○ ○ Green: ○ ○ ○ ● ○ ● ○ ●	Sensor is centring
Red: ○ ● ○ ● ○ ● ○ ● Green: ● ○ ● ○ ● ○ ● ○	Power failure waiting for auto-lock delay to time out (alternating red/green flashes).
Red: ● ● ● ● ● ● ● ● Green: ○ ○ ○ ○ ○ ○ ○ ○	Catastrophic failure: a sensor fault has made it impossible to complete the last operation.
Red: ○ ○ ○ ○ ○ ○ ○ ● Green: ○ ○ ○ ○ ○ ○ ○ ○	Locking system limit switch fault.
Red: ○ ○ ○ ○ ○ ● ○ ● Green: ○ ○ ○ ○ ○ ○ ○ ○	Horizontal tilt base limit. This could be a result of a poorly levelled sensor.
Red: ○ ○ ○ ● ○ ● ○ ● Green: ○ ○ ○ ○ ○ ○ ○ ○	The current operation timed out. This could indicate a fault or, in the case of centring, the sensor may need to be re-centred.