Thermo Fisher Scientific Alpha pH 800 - Manual (Page 29)

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7.3.4 Selecting a hysteresis (dead band) value
Hysteresis prevents rapid contact switching if your value is fluctuating near set
point. It does this by overshooting the set point value to a specified hysteresis
value. You can set the hysteresis value from 0.1 to 1.0 pH, 10 to 100mV.
Example: You have set your high set point at pH 9.0 and your hysteresis limit
value at pH 0.5. If your measured value overshoots high set point pH 9.0, the
controller’s relay activates, which in turn activates external devices such as a
pump or valve. The actions of the external device will cause the solution’s pH to
drop. When the pH drops to 8.5 pH, the relay and hence the pump will switch off.
1) Follow directions in 7.3.1 to enter Control
Relay mode.
2) Press ENTER key. Scroll with
Δ or ∇ keys
until upper display shows the hysteresis (dead
band) value and lower display shows “HYS”.
3) Press
Δ or ∇ keys to enter your hysteresis value for Set point 1 (Set point
2). Your controller will activate at the value you select.
4) Press ENTER key to confirm your selection.
5) Proceed to 7.3.5 step 3, or return to Measurement mode by pressing
Δ and
∇ keys simultaneously (escape).
NOTE: Please refer to Appendix 3 for a graphical representation of the
Hysteresis.
0.50
pH
HYS
SETUP
HOLD