LTH Electronics HPT63, Руководство по эксплуатации

Страница: 33 / 68

8 Set Point Relays
25
8.3.3 Pulse Proportional Mode
The Pulse Proportional (or PP) mode is intended to drive solenoid type dosing pumps
which have the facility to accept an external pulse input. The proportional band
operates in the same way as the Time Proportional mode. The output relay now
operates by producing a series of pulses of fixed duration. The pulse rate increases
as the measurement moves further from the set point, until it reaches the maximum
frequency at the limit of the proportional band (i.e. 4.2 pH in the previous example).
8.4 Dose Alarm Timers
The dose alarm timer can be used to prevent overdosing under many different fault
conditions , such as sensor failure or wiring faults. When the timer is enabled the
user can set the
Alarm Time . If the associated relay remains energised for longer
than the Alarm Time the alarm will activate, de-energising the relay to prevent over-
dosing and flash the set point LED on the front panel. The display will also flash a
warning message when the alarm is activated.
Note: During pulse or time proportional operation, the cumulative on-time that the
set point is active will be taken.
To cancel the warning, and reactivate the set point, press the key on the front
panel.
Note: If more than one Alarm is active, set point 1 takes priority over set point 2 and
they are cancelled in that order by additional presses of the key.
8.5 Alarms
The two set point relays can be configured as an alarm output triggered by one of the
following events:
•
Sensor error
•
Dose alarm
•
Calibration – when a calibration is in progress.
•
Off-line – unit has been taken off line, e.g. for servicing.
•
Any error – when any system error is detected.
To set an alarm output, choose the SP1 or SP2 menu, select Alarm from the menu
options and then select the required trigger.
8.6 Cleaning
The Cleaning menu options allow a set point relay to be used for controlling a device
for cleaning the sensor. For information on sensor cleaning, refer to Section 13.