# Measuring with external measuring hardware

Interface for external measuring hardware
Description | The CNC informs the PLC about the initialisation, start or end of a measurement run via the external measuring interface. The PLC prepares the external measuring hardware and activates or deactivates it. In order to use a switchable measuring probe, EXT_PROBE_WITH_DRIVE must be selected, otherwise PLC_EXT_LATCH_CTRL.

(see P-AXIS-00516 or [PROG//Extended programming])

Data type | LcControlExtLatchControl
Special features | This interface is only used to control the activation and deactivation of external measuring hardware.

- PLC_EXT_LATCH_CTRL: The CNC receives information about the measured value or the detected probing position via the control units probing_signal or probing_position.
- EXT_PROBE_WITH_DRIVE: Probing position via drive interface

Access | PLC writes please_rw + done_w
ST path | gpAx[axis_idx]^.ext_latch_control
Command
ST element | .please_rw
Description | When please_rw is set, the CNC signals to the PLC to prepare, activate or deactivate the external measuring hardware since a measurement run was started, aborted or terminated.
Data type | BOOL
Value range | [TRUE, FALSE]
Special features | Consumption data item
Access | The CNC refreshes the data of the measuring interface only if this element is FALSE. After a refresh, the CNC sets this element to TRUE after the element done_w was set to FALSE. The PLC reads the data of the measuring interface if this element has the value TRUE. After the data is transferred, the PLC sets the value to FALSE.

Parameter
ST element | .ext_latch_order_r
Description | The CNC signals to the PLC in this datum the required measurement parameters such as activate/deactivate the measuring function or the number of the measurement input.
Data type | HLI_EXT_LATCH_ORDER
Access | PLC is reading
Acknowledgement
ST element | .done_w
Description | By setting the element done_w to TRUE, the PLC signals to the CNC that the measuring job was executed. The measuring hardware is then ready, activated or deactivated.
Data type | BOOL
Value range | [TRUE, FALSE]
Special features | Consumption data item
Access | The PLC sets the value to TRUE if the measuring order was executed. The CNC sets the value to a FALSE before a new command.
Measuring order data
Description | In this parameter, the CNC signals to the PLC whether the measuring hardware is to be prepared, activated or deactivated. In addition, the CNC informs the PLC of the measurement channel to be used and the relevant measurement edge.
Data type | HLI_EXT_LATCH_ORDER
ST path | gpAx[axis_idx]^.ext_latch_control.ext_latch_order_r
Access | PLC is reading
Measuring order identifier
Description | ID of measuring order to be executed.
ST element | .order_id
Data type | UDINT
Value range | Constant | Meaning
HLI_EXT_LATCH_PREPARE_PROBE | The measuring hardware must be prepared (only EXT_PROBE_WITH_DRIVE)
HLI_EXT_LATCH_ENABLE_PROBE | Start of measurement run, the measuring hardware must be activated.
HLI_EXT_LATCH_DISABLE_PROBE | The measurement run was terminated or aborted by reset. The measuring hardware must be again deactivated/switched off
Access | PLC is reading

Number of probing input
Description | In this data item, the CNC signals to the PLC the input to be used for measuring (see P-AXIS-00517)
ST element | .input
Data type | DINT
Value range | Probing input 1 – 255 Probing input 1-2 (only EXT_PROBE_WITH_DRIVE)
Access | PLC is reading
Relevant measurement edge
Description | In this data item, the CNC signals to the PLC the relevant measurement edge (rising/falling) to be used for measuring (see P-AXIS-00518)
ST element | .edge
Data type | UDINT
Value range | Constant | Meaning
HLI_MEAS_SIGNAL_LOW_ACTIVE | The measured value is to be detected on the falling edge.
HLI_MEAS_SIGNAL_HIGH_ACTIVE | The measured value is to be detected on the rising edge.
Access | PLC is reading

## Signal profile with PLC_EXT_LATCH_CTRL

The block diagram below shows an example of the signal profile of the control units ext_latch_control, probing_signal and probing_position during a measurement process with external hardware:

Example of signal profile of measurement with external hardware

## Signal profile with EXT_PROBE_WITH_DRIVE

The block diagram below shows an example of a measurement process using switchable external hardware:

Signal profile with switchable external hardware

## Notice

When the external measuring interface is used, the probing signal of the probing_signal control unit is not dependent on the relevant measurement edge P-AXIS-00518. A positive edge always signals the successful detection of a measured value in the external measuring hardware.

## Notice

If the control unit probing_position is not enabled when the measurement event occurs, the CNC uses the actual position of the axis as measurement value at the time stamp of the probing signal occurrence.