Thermo Fisher Scientific Alpha pH 190 (In the process of updating the brand guideline & product image) - Manual (Page 38)

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Appendix 1: Asymmetrical / Symmetrical Mode
The Alpha pH 190 controller can be operated in the
asymmetrical or symmetrical modes (See Set up Program
P3.2).
Asymmetrical mode:
Asymmetrical mode works well in environments where
there is little or no electrical noise. When there is noise,
the noise acts as a common signal, which is picked up by
both the pH and the reference electrodes.
However, since the reference electrode is grounded to the
ground potential of the amplifier, electrical noise will be
present only on the pH electrode. This noise is amplified
along with the pH signal, which causes fluctuations in the
pH or ORP readings.
Electrical noise from a DC source (as in an electroplating
tank) will typically result in stable but incorrect values.