Idle Mode; Last Calibration Data Viewing Mode - Hanna Instruments HI 720 Instruction Manual

The Fail Safe mode is accomplished by connecting the external alarm circuit
between the FS•C (Normally Open) and the COM terminals. This way, an alarm
will warn the user when measurement overtakes the alarm thresholds, power
fails, or the wire connecting the process meter with the external alarm circuit
breaks.
Note To activate the Fail Safe feature, an external power supply must be
connected to the alarm device.
Control through Analog Output
Instead of configuring relays, it is possible to use an output signal (selectable at
0-20 mA or 4-20 mA, and proportional to the PID action) at the analog output
terminals.
With this output, the actual output level amplitude varies continuously (with an
update delay of 5 seconds) between the maximum and minimum values, rather
than varying the proportion of ON and OFF times (duty cycle control). The
output signal range can be selected through setup items O.11 (output #1) and
O.21 (output #2).
A device provided with analog input (e.g. a pump with a 0-20 mA input) can be
connected to these terminals. The analog output #1 is associated to the setpoint
#1, and the analog output #2 to the setpoint #2.
For a control through analog output, a setpoint has to be configured to
"PidL" or "PidH", and the corresponding output has to be set to "Control" (setup
item O.10 for analog output #1, and O.20 for analog output #2). In this case
no relay can be associated with the same setpoint being used for the control.
On the other hand, if a control through analog output is already associated
with a setpoint, it is not possible to configure a relay to the same setpoint.
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I M
DLE ODE
While in idle mode, the device only performs measurements. It does not activate
relays or generate a control signal to the analog output(s).
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, while the yellow LEDs are OFF .
The alarm relay could be de-energized upon an error (whether that happens or
not, depends on the customized alarm configuration; see "Alarm" section for
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 when an error occurs.
The idle mode is useful to disable control actions when the external devices are
not properly settled or whenever any fault circumstance is detected.
L C D V
AST ALIBRATION ATA IEWING
The following data about the last calibration is stored in the EEPROM:
• Date & time of last conductivity calibration
• Calibration point(s)
• Cell constant or installation factor value
To view the last calibration data, press the CAL DATA key. To quit and return to
normal operations, press CAL DATA again.
Note When the "Input selection" item is set to "Digital Transmitter", the
last calibration data displayed, refers to the Digital Transmitter and
is stored in that device. The calibration data of the process controller
is kept in its internal memory and comes back when the "Input se-
lection" item is changed again to "Inductive probe".
M
ODE
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