Control Mode - Hanna Instruments HI 504 Instruction Manual

CONTROL MODE

The control mode is the normal operational mode for this meter.
During control mode HI 504 fulfills the following main tasks:
• convert information from pH/ORP and temperature inputs
to digital values and show them on the display;
• control relays and generate the analog outputs as deter-
mined by the setup configuration;
• display alarm condition;
• perform cleaning actions according to the relays configuration;
• start and stop hold mode according to the programmed
control timing;
• RS485 management.
In addition, the meter can log working data through RS485
connection. These data include:
• pH, mV and
• last calibration data;
• setup configuration (also from a remote workstation);
• event data.
In a normal situation, during control mode, the green LED is
ON and the error LED (red) 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 deactivate the control mode set CONTROL ENABLE to
"OFF" in setup menu (CONTROL ("CtrL") group).
When measurements are in overflow, the upper or lower range
limit is shown on the LCD with blinking digits.
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, "rECO");
2. setpoint 2 (Analog output #2 must be set to recorder, "rECO");
3. simple cleaning;
4. hold mode.
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o C measured values;
In the first two cases the configuration of Setpoint (1 or 2)
determines the operating mode of the relay. Once enabled,
the control relay can be configured to control as a ON/OFF
or PID control of the acid/base dosage.
A High-hight Alarm is imposed for acid/base dosage time
when the relays are energized continuously. 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 device stays in alarm condition until
relay is de-energized.
If the "hold mode" is selected for the relay, then it is ener-
gized only when the meter is in hold mode. In this case there
is no time boundary for the ON state of the relay.
The option for relays 3 and 4 can be configured to opera-
tions in three modes:
1. simple cleaning;
2. advanced cleaning;
3. hold mode.
ON/OFF CONTROL MODE
Once a relay is enabled (set 1, set 2), the setpoint can be
configured to be activated as a high limit ("OOHI") or as a
low limit ("OOLO"). In both cases the following values have
to be defined through setup:
• setpoint value (pH/mV; setup item C.11 or C.21);
• hysteresis for setpoint (pH/mV value; setup item C.12 or C.22).
A control device can be wired to the contact output.
Connect the device to the COM and NO
(Normally Open) or NC (Normally
Closed) terminals of the relay.
The ON relay state occurs when relay is energized (NO and
COM connected, NC and COM disconnected).
The OFF relay state occurs when relay is de-energized (NO
and COM disconnected, NC and COM connected).
The following graph shows relay state along with pH mea-
sured value (similar graph can be derived for mV control).
As shown below, when the measured pH exceeds the setpoint
threshold, the relay(s) is (are) energized, until the pH mea-
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