PART THREE - OPERATION
SECTION 7 - RELAY OVERFEED TIMER FEATURE
Rev. 2-300
Accu4™ Low-range Turbidimeter System
69
S
ECTION
7
7.1 Why Use an
Overfeed Timer
7.2 Configuring Relay
Overfeed Timers
7.3 Overfeed Timer
“Timeout” Operation
7.4 Resetting Overfeed
Timers
7.5 Interactions with Other
Analyzer Functions
The useful relay overfeed timer feature,
only available to a
CONTROL function relay,
is described in more detail in
this section.
Suppose that you configure a CONTROL relay with a high
phase to operate in response to increasing measured tur-
bidity. The CONTROL relay will then turn on whenever the
measured turbidity exceeds its preset setpoint. When the
measured turbidity decreases below the setpoint by an
amount you preset (the deadband setting), the relay will
turn off. But what if a damaged sensor or a process upset
condition keeps the measured turbidity above the setpoint
or deadband setting? The control element (valve, pump,
etc.) switched by that relay would then continue to operate.
Depending on the application control scheme, this may ex-
cessively dispense costly chemical additives or overly drain
or divert the process. Also, the control element itself could
be damaged due to excessive continuous or unusual op-
eration such as a pump that is running dry. The useful
overfeed timer prevents undesirable conditions like these
from happening. It restricts how long the relay and its con-
nected control element will remain on regardless of conditions.
To set a relay overfeed timer, use its respective configura-
tion menu screen. The time you set to restrict how long the
relay stays on (0-999.9 minutes) should be just enough to
provide acceptable results. An excessive setting may waste
chemicals or the process itself. Initially, set this time as an
estimate. Then, by experimenting and observing the re-
sponse, periodically “fine tune” to optimize the setting.
When a CONTROL relay is on and its overfeed timer “times
out,” its annunciator will blink. This indicates that the relay
is now off and will remain off until you manually reset the
overfeed timer. After reset, the relay annunciator stops
blinking. (All overfeed timers are reset simultaneously.)
To manually reset all relay overfeed timers, please refer to
Part Three, Section 6.3.
A relay overfeed timer can, and often will, interact with other
analyzer functions while those functions are in use. Table C
on the next page explains common overfeed timer interac-
tions.
RELAY OVERFEED TIMER FEATURE
