Thermo Fisher Scientific Alpha pH 200 (In the process of updating the brand guideline & product image) - Manual (Page 34)

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Appendix 1: Asymmetrical / Symmetrical Mode
The alpha pH 200 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.