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averaging setting controls how many readings are averaged to form the output value. The pressure
averaging time defaults to 5 seconds and can be set from 1 to 60 seconds. The value effectively filters the
output to prevent noise and false alarms.
The device also compares the output pressure value to the alarm set-points and takes appropriate
action. If the pressure value exceeds either set-point then an alarm condition is set and the device will
operate in alarm mode. Alarm mode activation is controlled by certain delay times and user settings
described later. The device also monitors the keys and takes appropriate action if a key is pressed.
ALARM OPERATION
The alarm feature includes an on-board buzzer, silence switch, control relay, remote buzzer connection
and LED.
The alarm feature has several settings that can be controlled by the setup menu. The device has two
alarm trip points designated the high pressure alarm limit and the low pressure alarm limit. The high
pressure alarm defaults to 50% of the maximum pressure range and the low pressure alarm defaults to
50% of the minimum pressure range. For example, if the device is set to a ±1"wc range, then the default
low pressure alarm limit will be -0.5 "wc and the default high pressure alarm limit will be +0.5 "wc. This is
the same result for Pa ranges.
The alarm set-points can be set over the pressure range with certain conditions. For this example the
pressure range is ±1"wc.
• the low pressure alarm limit cannot go below the minimum pressure range setting (-1.0"wc)
• the high pressure alarm limit cannot go above the maximum pressure range setting (+1.0"wc)
• the high pressure alarm limit must always be greater than the low pressure alarm limit
• the minimum alarm span (high alarm - low alarm) must be at least 25 % of the pressure span (2"wc x
25 % = 0.5"wc)
• if the minimum span is reached while adjusting one of the alarm limits, then the other alarm limit will
be "pushed".
In this example for the ±1"wc range, these are some possible alarm settings: -1.0 to 0.5"wc, -0.75 to
-0/25"wc, -0/5 to 0"wc, -0.25 to 0.25"wc, 0 to 0.5"wc, 0.5 to 1.0"wc.
The alarm also has settings for on delay and off delay which can be set via the menu. Both of these
default to 5 seconds but may be changed from 1 to 59 seconds or 1 to 10 minutes. For an alarm
condition to be set the pressure value must exceed either alarm trip point for more than the alarm on
delay time. For an alarm condition to be reset the pressure value must return to a non-alarm value for
more than the alarm off delay time.
When an alarm condition is set the red LED with flash, the relay output will activate, the local buzzer will
sound and the remote buzzer output will activate. If the alarm condition is reset, all four outputs will
deactivate. The LED flashes at a rate of 1 second on / 1 second off, the relay and remote buzzer are held
on and the local buzzer sounds at a rate of 1 second on / 5 seconds off.
The alarm can be silenced by pressing the front cover silence switch during an alarm condition. In this
case the buzzers and relay will de-activate but the LED continues to flash until the alarm condition is
removed. The alarm silence time can be set in the menu or via BACnet® to 1-60 minutes or forever, and
the default is 30 minutes. This means that if the silence switch is pressed and the alarms are silenced (and
the alarm condition is not reset) then the alarm will re-activate after the silence time has expired. For the
default setting of 30 minutes, the alarm buzzers and relay will activate again after 30 minutes of silence
if the alarm condition still exists. If the delay is set to forever, then the alarms will not activate again in
silence mode until the alarm condition is cleared and another alarm condition is set.
The alarm can be disabled by the user by holding the front cover silence switch for 5 seconds. It can be
re-enabled by holding the switch again for 5 seconds. When the alarm is disabled, the OFF icon will be lit
on the LCD and no alarms will be activated.
