Figure 2 shows the wash logic as a flow diagram. The automatic prism wash cycle described below consists of three 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 one-second 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 from the user interface at 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 two 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. Similarly, 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, see Figure 3. The specified wash time is never exceeded.
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:
- Under the diagnostic message NO SAMPLE, as this 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, see Configuring input switches, indicating, for example, that there is no process flow. The diagnostic message is EXTERNAL WASH STOP.
- 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.
| Remote wash is triggered at the closing of the switch. If the switch is held closed, only one wash cycle is carried out. |
| The wash is inhibited if there is no sample, no sensor or the sensor cannot measure correctly. |
