Thermo Fisher Scientific Alpha pH 100 - Manual (Page 21)

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7. Additional Information
The controller allows you to set High and Low alarms that
switch on or off relays, and activating or deactivating devices
linked to the controller. In cases where the pH/ORP values
fluctuate close to the high or low setpoints, the relays will
continuously switch on/off very quickly and may cause
problems to the linked devices. The hysteresis band allows you
to set an allowable range of fluctuations to prevent the relays
from activating and deactivating too quickly. See below.
It is not possible to set the high set point lower than the low set
point and vice versa (taking the hysteresis band into
consideration). For example, when the high set point is 8.50
pH and the high hysteresis band is set at 0.40 pH, then the low
setpoint cannot be set at higher than 8.50 - ½ Hi HYS.
NOTE : The shaded area indicates the hysteresis band.
Hi
Hys
Lo
Hys
Hysteresis Band
Hysteresis Band
Hi
Set
Lo
Set
pH
Actual
A
B
C
D
E
F
G
H