Hanna Instruments HI 504 - Manual (Page 28)

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HOLD MODE
This function is started by:
• calibration;
• setup;
• cleaning in place;
• the hold digital insulated input
1 when it is on; normally,
the signal level is polled at least every 4 seconds;
• the proper key combination ( and æ keys together) for
service; the same key combination is used both to start
and to stop the hold mode (the key combination acts as
the hold digital input). To activate the hold mode in this
way, password is required;
• the daily programmable control timing (see setup items
C.41 through C.57);
• an error event (see also the “Alarm - Error Configuration”
section);
• the hold start/stop RS485 command;
• the service hold (Calibration and Setup) in the Digital Trans-
mitter.
During hold mode, control and control relays are disabled.
If the meter is in idle or control mode
and displaying measurements, the last
measured value (both for temperature
and pH/ORP) is frozen on the display;
the secondary LCD shows “HLd”;
the temperature value can be displayed on the secondary
LCD by pressing and holding the key; when the key is
released the “HLd” message comes back on the secondary
LCD.
If the pH or mV or temperature values
are not available because the meter
did note take any measurement be-
fore going to hold mode, then the
primary or the secondary LCD shows
dashes.
1 There are two digital insulated inputs: one for hold mode and one for advanced cleaning.
IDLE MODE
During idle mode the device performs only measurements
but it does not activate relays in order to control the process
or let out a control signal to the analog output.
In a normal situation the alarm relay is energized (no alarm
condition) and the green LED is ON, the red LED is also fixed
ON to warn users the device is not controlling the process,
the yellow LEDs are OFF.
Moreover, the alarm relay could be de-energized upon an
error (whether that happens or not, depends on the custom-
ized alarm configuration; see “Alarm” section for more details).
Nevertheless, the error due to alarm threshold overtaking
does never generate an alarm during idle mode since all the
control functions have been disabled by the user.
The red LED flashes in any case upon an error.
Idle mode is useful to disable control actions when the exter-
nal devices are not properly settled or whenever any fault
circumstance is detected.
To set the meter to idle mode it is sufficient to disable the
control mode (setup item C.00 to “OFF”).
When measurements are in overflow, the upper or lower range
limit is shown on the LCD with blinking digits.