The automatic prism wash cycle consists of 3 phases: precondition, wash and recovery. The optional preconditioning function is used to, for example, blow out the condensate before washing. After the preconditioning there is a 1 s pause to avoid having both precondition and wash relays active at the same time.
The wash cycle is initiated when the wash interval has elapsed. The wash can also be started by closing an external switch, see Configuring input switches, or manually on the SENSOR STATUS display, see Testing prism wash.
The order of priority for these wash triggers is as follows:
- Manual wash
- Remote wash request
- Wash interval timer
| For safety reasons 2 sensors never wash simultaneously. If the manual wash button for sensor A is pressed while sensor B is washing, the wash cycle for sensor A is started after B has finished. If the interval time for sensor B elapses when A is washing, the wash for sensor B is delayed until A has finished. |
In case of remote wash request the request is discarded if it arrives when the other sensor is washing. The request is honored only if the contacts are held closed until the other sensor has finished.
The wash relay is closed for the wash time specified in the wash settings. If the wash auto-cut functionality is active, the wash may be ended earlier. The specified wash time is never exceeded. For more information, see Wash cycle.
After the wash phase is completed, a recovery time is spent. During the wash cycle (precondition, wash, recovery) the measurement result is in hold unless otherwise specified.
Preventing automatic wash
The preconditioning and wash relays are never activated by the automatic wash control in the following situations:
- The diagnostic message NO SAMPLE is shown, as it indicates a clean prism in an empty process line. The diagnostic message is WASH STOP/NO SAMPLE.
- If a wash stop input switch is closed, indicating, for example, that there is no process flow. The diagnostic message is EXTERNAL WASH STOP. For more information, see Configuring input switches.
- If the process temperature limit is activated and the temperature falls below the limit, indicating that the process is not running. The diagnostic message is LOW TEMP WASH STOP.