Control Mode - Hanna Instruments HI 720 Instruction Manual

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The control mode is the normal operational mode for this meter. During control
mode HI 720 fulfills the following main tasks:
• convert information from conductivity and temperature inputs to digital values,
and show them on the display
• control relays and generate the analog outputs as determined by the setup
configuration
• display alarm condition
• perform cleaning actions according to the relay configuration
• start & stop hold mode according to the programmed control timing
• RS485 management
In addition, the meter can log working data. These data include:
• conductivity and
• last calibration data
• setup configuration
• event data
While in control mode, in a normal situation, the green LED is ON and the red
(error) LED is OFF. The red LED is never fixed ON, and blinks only upon an error.
The green LED is associated to the alarm relay and is OFF if the alarm is active.
To disable the control mode, set the "Control Enable" setup item to "OFF" ("Con-
trol" setup group).
Relay Modes
There are four relay options that can be configured through the setup menu to
perform different tasks.
Once enabled, relays 1 and 2 can be used in four modes:
1. setpoint 1 (Analog output #1 must be set to "Recorder")
2. setpoint 2 (Analog output #2 must be set to "Recorder")
3. simple cleaning
4. hold mode
If option 1 or 2 is selected, the setpoint configuration determines the relay oper-
ating mode. Once enabled, the relay can be configured as a ON/OFF or PID
control of the dosage.
An alarm limit is imposed for dosage time when the relays are energized con-
tinuously. This parameter can be set through setup procedure ("Control" group,
setup item C.32).
When the upper time boundary is reached, an alarm is generated and the device
will remain in alarm condition until the relay is de-energized.
C measured values
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