YOKOGAWA PH200 User Manual

IM 12B6C2-E-H
4-4. Sensor selection and diagnostics
The inputs of the EXA PH200 transmitter are
free programmable for ease of retrofit on
existing installation. Standard glass pH-elec-
trodes, Ag/AgCI reference electrodes and
Pt100 sensor need no programming. If there
is a mismatch of the sensors connected a
fault will be indicated with a signal field on
the display and if activated by a 22 mA
signal.
4-4-1. Selection of measurement and
reference electrode
The EXA PH200 is preprogramed to ac-cept
industry standard glass electrodes and refe-
rence electrodes. Checks for asymmetry-
potential and slope are implemented during
calibration. The on-line impedance check on
both sensors is not initialized unless activa-
ted from the service level §7-5. The EXA is
suitable for all type of electrodes (e.g.
Enamel, Antimony). In §7-3 the specific
Isothermal point of intersection (ITP), slope
(pH/mV) and asymmetry potential can be set
for each type of electrode.
4-4-2. Selecting a temperature sensor
The EXA PH200 has been factory set for a
Pt100 temperature sensor to DIN standards.
This will give satisfactory results when the
normal electrode cable length is used. To
correct for cable resistance it is possible to
calibrate the sensor from the service level
(zie §7-11).
The highest accuracy is obtained by using a
Pt1000 element with the EXA PH200 trans-
mitter. This element gives a ten-fold increase
in resistance dependance over a Pt100 sen-
sor. Setting the instrument for Pt1000 is
from the service level at §7-4.
4-4-3. Off-line calibration checks
The EXA PH200 transmitter incorporates a
checking of the asymmetry-potential after a
calibration has been performed. This is valid
for both manual or automatic calibration.
The actual value can be called up from the
display routine in the maintenance menu
(AS). A large value can indicate a poisoning
of the reference system used. If the asym-
metry-potential exceeds + 120 mV or
-120 mV an error E2 will be generated.
To disable this checking see §7-5.
The EXA PH200 also checks for the slope of
the pH sensor after automatic calibration
has been performed. The actual value of the
slope can be called up from the display rou-
tine in the maintenance menu (SL). The
value is an indication for the "ageing" of the
sensor. If the value stays within the limits of
70 to 110 % of the theoretical value of
59.16 mV/pH at 25°C it is accepted.
Otherwise an error E3 is generated. Disable
this testing from the service level §7-5.
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YOKOGAWA PH200 Specifications

General

Brand	YOKOGAWA
Model	PH200
Category	Measuring Instruments
Language	English