35
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
greatest accuracy, it is recommended that the instrument is
calibrated frequently.
It is possible to standardize the electrode with only one buf-
fer, preferably close to the expected sample value (one-point
calibration), but it is always good practice to calibrate in
at least 2 points.
pH CALIBRATION (for HI21 Series only)
The pH controller can be calibrated through a one-point,
two-point or three-point calibration. You do not need to
enter the method chosen, simply exit
the calibration mode, by pressing
CAL, when the desired number of
points has been calibrated.
The calibration points for HI21 are pH4.01, pH7.01 and
pH10.01 (at 25 °C). The sequence proposed by the con-
troller is pH7.01, pH4.01, pH10.01. 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 indications on the display during the calibration pro-
cedure.
Initial Preparation
Pour small quantities of pH7.01
(
HI7007
) and pH4.01 (
HI7004
)
and/or pH10.01 (
HI7010
) solutions
into individual beakers. If possible,
use plastic beakers to minimize any
EMC interference.
