Hanna Instruments HI 720 Series User Manual

Page 19

ONTROL

ODE

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 val-

ues, 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

C measured values

• 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 de-
vice will remain in alarm condition until the relay is de-energized.

• Use a Checktemp or another calibrated thermometer with a resolution of 0.1°

as reference thermometer, and immerse the temperature sensor in the ice
bath as near to the Checktemp as possible.

• Confirm the calibration option and the instrument will start the automatic

calibration of the first point.

• When the reading becomes stable, the instrument will ask confirmation.
• Press CFM to confirm and proceed with the second point, or CAL to exit with-

out saving.

• Select the desired value for the second point (25°C or 50°C) by using the up &

down arrow keys. Immerse the temperature sensor in the proper temperature
bath as near to the Checktemp as possible, confirm the desired calibration
point and the instrument will start the automatic calibration of the 2nd point.

• When the procedure is completed, the meter will ask for confirmation. Press

CFM to save the calibration, or CAL to exit without any updating.

Analog Output Calibration (Analog Outputs 1 & 2)
The instrument can be provided with one or two analog outputs, each of them
can be calibrated at 2 points (4 and 20 mA).
• Connect an Ammeter or the HI 931002 tester to the analog output to mea-

sure the current erogated by the meter.

• Select the desired calibration mode by using the up & down arrow keys, and

confirm the choice by pressing CFM. The instrument will show the first cali-
bration value (4 mA).

• With the tester check the real current value provided by the instrument at the

output port. If this value is different from the expected one, adjust it with the up
& down arrow keys, until it matches with the first calibration point. To increase
the adjustment speed when the displayed value is far from the calibration one,
press and hold the arrow keys.

• Press CFM to confirm and turn to the second cali-

bration point (20 mA), then proceed as for the
first point.

• Press CFM to save the calibration, or CAL to exit

without any updating.