Hach 900 MAX Section, Set Point Alarm Conditions, Level, Flow, Analog Channels 1–3, Deadband

Section 6

1.Enable one of the alarm conditions.

2.Select an action to occur when the alarm is activated.

3.Set either a High trip point or a Low trip point.

4.After entering the trip point enter the deadband value. The deadband is the area between the alarm “turn on” and “turn off.”

Note: Log rainfall to use an alarm on a rainfall condition; likewise, log flow in order to

	implement an alarm on a flow rate of change.
Set Point Alarm Conditions:
•	Level	•	Cabinet Temperature (refrigerated samplers)
•	Flow	•	Analog Channels 1–3
•	Flow Rate of Change	•	Analog Ch. 4 or D.O.
•	pH	•	Analog Ch. 5 or D.O. Temp.
•	ORP	•	Analog Ch. 6 or Conductivity

•Process Temperature • Analog Ch. 7 or Conductivity Temp.

•Rainfall

Note: Rainfall and Flow Rate of Change alarms are HIGH set point conditions; they take no deadband and they are time dependant.

Deadband

After entering the trip point, enter a deadband value. The deadband is the area between alarm “turn-on” and “turn-off”.

The purpose of setting the deadband is to eliminate alarm chatter which may occur if the “turn-on” and “turn-off” values are too close together. Small fluctuations occurring when the reading is at or near the trip point can rapidly toggle an alarm relay on and off.

In the pH example (Figure 28) the deadband is set to 0.10 pH. When the pH reached 6.9 (lower dashed line), the alarm tripped, but the alarm did not turn off until the pH came back up to 7.00. This difference is the deadband setting which should be set according to the characteristics of the item

being measured.

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Alarm Relays	8990cm.fm