35
34
CALIBRATION
The controller is factory calibrated for mV and temperature
inputs as well as for the analog outputs.
The user should periodically calibrate the instrument. For great-
est accuracy, it is recommended that the instrument is calibrated
frequently.
It is possible to standardize the electrode with only one buffer,
preferably close to the expected sample value (one-point cali-
bration), but it is always good practice to calibrate in at least
2 points.
pH CALIBRATION (for HI 21 Series only)
The pH controller can be calibrated through a one-point,
two-point or three-point calibration. You do not need to en-
ter the method chosen, simply exit the
calibration mode, by pressing CAL,
when the desired number of points has
been calibrated.
The calibration points for HI 21 are pH 4.01, pH 7.01 and
pH 10.01 (at 25°C). The sequence proposed by the control-
ler is pH 7.01, pH 4.01, pH 10.01. However, the user can
change this sequence by means of the and keys.
The electrode must be kept hydrated at all times and defi-
nitely prior to calibration. The temperature probe should also
be connected to the process meter. The meters are equipped
with a stability indicator. The user is also guided with indica-
tions on the display during the calibration procedure.
Initial Preparation
Pour small quantities of pH 7.01
(
HI 7007
) and pH 4.01 (
HI 7004
)
and/or pH 10.01 (
HI 7010
) solutions
into individual beakers. If possible, use
plastic beakers to minimize any EMC
interference.
HI 7007
HI 7004
HI 7004
If asking for last calibration data and the controller was never
calibrated, it answers with “0”; e.g. “
01<STX>0<ETX>
”.
If the controller was calibrated, it answers with “1” followed
by the calibration data. The
Data
field of the answer has the
following format:
HI 21
:
1<Date>
<
Time
><
Offset
><
Slope1
><
Slope2
><
Buf1
><
Buf2
><
Buf3
>
•
Date
:
DDMMYY (e.g. “170400” for April 17,2000)
•
Time
:
HHMM (e.g. “1623” for 4:23 pm)
•
Offset
: ASCII string (e.g. “-0.2”)
•
Slope 1
: ASCII string (e.g. “62.5”)
•
Slope 2
: ASCII string (e.g. “60.4”)
•
Buf 1
:
ASCII string (e.g. “7.01”)
•
Buf 2
:
ASCII string (e.g. “4.01”)
•
Buf 3
:
ASCII string (e.g. “10.01”)
HI 22
:
1<Date>
<
Time
><
Buf1
><
Buf2
>
•
Date
:
DDMMYY (e.g. “170400” for April 17,2000)
•
Time
:
HHMM (e.g. “1623” for 4:23 pm)
•
Buf 1
:
ASCII string (e.g. “7.01”)
•
Buf 2
:
ASCII string (e.g. “4.01”)
The items in the
Data
field are separated by blanks.
If an item is not available (e.g.
Buf 3
if only a two points
calibration was performed) it is replaced by the “N” charac-
ter.
Note
The “r485” message can appear on the LCD while the con-
troller is receiving or answering commands.
SETTING THE BAUD RATE
The transmission speed (baud rate) of the meter and external
device must be the same.
The meter is factory set to 9600 bps. To change this value,
use setup item 71.
