YOKOGAWA PH202G (S), User Manual

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IM12B07D02-01E
Parameter setting 5-11
5-3. Notes for guidance in the use of service coded settings
Don't set or input service code numbers other than the code numbers defined in this manual. Setting an
undefined service code may make the transmitter malfunction.
When an undefined service code is input by some accident, push the MODE key and escape from the
service level.
5-3-1. Parameter specific functions
Code 01 *pH/ORP Choose the main measuring parameter. The option of the ORP input is used
with an inert metal electrode as measuring sensor which gives a reading
directly in millivolts. This signal can then be interpreted to give information
about the oxidation state of the process solution, and derived information like
the absence of a compound (like Cyanide for example which is destroyed in
oxidizing solutions).
Code 02 *PRM.2 Enable the use of a second measuring parameter simultaneously with pH (the
main parameter).
With the correct sensor (e.g FU20), ORP measurement is possible as
parameter 2 With the same sensor, rH measurement is possible as parameter
2, this is calculated from pH and ORP and is a value which gives the oxidizing
power of the solution while compensating for the effect of pH.
This function is particularly useful for applications where both the pH and
oxidation-reduction potential of the process need to be known. The availability
of both measurements in a single system is convenient.
Note that in both cases a suitable sensor combination is needed to make this
possible. The Yokogawa FU20 (4-in-1) sensor can be used for this purpose, or
a combination of individual sensors. Contact your local Yokogawa sales office
for advice regarding applications and sensor selection.
Code 03 & 04 *Z1.CHK The EXA PH202 has an impedance check capable of monitoring the impedance
& *Z2.CHK of all sorts of sensor systems. In order to “fine tune” this diagnostic tool it is
necessary to set it up to match the sensors used. The default settings give a
good setup for a conventional system comprising pH glass sensor and a
reference electrode, either as individual electrodes or as a combination style
sensor. The impedance limits will need to be adjusted to get the best from
systems using heavy duty, or fast response electrodes.
The impedance measuring system has a very wide span requirement. As it can
measure in k Ω and also in G Ω (10
9
) there are hardware switches to set high
range (1M Ω to 2 G Ω ) or low range (1k Ω to 1M Ω ) measuring. As a default the
system is set to measure high impedances on input 1 (the one normally
used for the pH glass sensor input) and low impedances on input 2 (the one
normally used for the reference input). Examples of where these settings need
to be changed from the default, are Pfaudler enamel sensors which need two
high impedance settings, and Platinum sensors with a standard reference,
which need two low impedance settings.
The temperature compensation of the impedance measurement is for conven-
tional pH glass sensors. When other sensors are used, switch this feature off.
Code 05 *CAL.CK The calibration checking feature, when enabled, gives security against entering
wrong calibration data. For example when aged sensors are due for
replacement, the EXA flags an error message and prevents a calibration being
completed where the subsequent measurement can only exhibit errors and
drift.
Limits are set for the maximum permissible Asymmetry potential, and Slope.