Hold Mode - Hanna Instruments HI 720 Instruction Manual

HOLD MODE

This function is started by:
• calibration
• setup
• cleaning in place
• the hold digital insulated input (there are two digital insulated inputs: one for
hold mode and one for the advanced cleaning) when it is on; normally the
signal level is polled at least every 4 seconds
• the proper key combination (CFM and up arrow keys together) for service; the
same key combination is used both to start and stop the hold mode (the key
combination acts in the same way as the hold digital input
• the daily programmable control timing (see setup items C.41 to C.57)
• an error event (see also the "Alarm - Error Configuration" section)
• the hold start/stop RS485 command
During hold mode, control and control relays are disabled. If the meter is in idle
or control mode and displaying measurements, then the last measured value
(both for temperature and conductivity/concentration) is frozen on the display.
During hold mode, the LCD shows the "Hold" message.
If the conductivity/concentration or temperature val-
ues are not available because the meter did not per-
form any measurement before going in hold mode,
then the display shows dashes.
All alarm signals (red LED, alarm relay, fault currents) are suspended while in
hold mode (the correspondent errors are not closed), unless the hold mode has
been triggered by an error (and no other trigger source is active).
If the hold mode is triggered by an error, and that error is related to measure-
ments (e.g. conductivity input overflow), the instrument continues to measure in
order to track the possible error closing, even though the display continues to
show the hold value.
The analog output follows these rules:
• If it is configured for control (i.e. setup item O.10 or O.20 has been set to
"Control-setpoint 1" or "Control-setpoint 2", respectively), then its value is set
to the minimum (e.g. 4 mA for 4-20 mA input)
• If it is configured for a recorder, then its value is either set to the user selection
(setup item O.15 or O.25, with O.14 or O.24 set to "User selected value") or
frozen to the output value just before entering the hold mode (with O.14 or
O.24 set to "Previous value").
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After the cause which made the instrument enter the hold mode expires, the
device exits the hold mode, but control and alarms remain disabled for a user-
selectable delay (0 to 99 seconds). In that situation, measurements are normally
acquired, displayed and recorded through the analog or RS485 output.
Note Alarms (alarm relay, red LED, fault currents) are not disabled if the
hold mode has been triggered by an error and no other trigger source
is active.
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