User manual

Digital Monitor AMC-1DBx Series User Manual
86
information for the
new transmitter into
the monitor database.
new transmitter into the monitor database.
• Use AMC Manager as an alternative when
configuring the monitor from the front panel.
5. Set the monitor’s
appropriate RS-485
Interfaces to “Admin
Enable” mode.
6.13.3 Downstream MODBUS Timeout.
The MODBUS protocol provides error checking to ensure that messages that are received
are verified to be intact and error free. However, errors can occur on the RS-485 interface,
which cause the messages to fail the error checking by the receiver of the message. This
results in either the transmitter not ‘seeing’ a message from the monitor, or the monitor does
not ‘see’ the response to a message.
For this reason, when the monitor fails to receive a response from a transmitter, the
message will be sent up to 2 times, - the original message plus one retry – before
moving to the next transmitter.
• When the monitor discards frames due to error checking, the sensor will appear
as fail in the sensor display and the monitor enters fail state.
• Considerations: disable a transmitter that requires too many retries.
12. Sensor Activation Delay. When gas concentration crosses a given alarm threshold, the
alarm is not activated until the concentration remains above the threshold for the
Activation Delay period of time. If the gas concentration falls below the alarm threshold,
then the channel activation timer is cleared. The activation delay is set in seconds. Use
of the activation delay avoids reacting to temporary transients and/or noise from the
sensor.
13. Minimum Run Timer. After gas concentration decreases/increases to below/above the
Threshold (subject to hysteresis), the relay is kept activated for a minimum period of time
defined in the Minimum Run Timer. The minimum run timer ensures that the external fan
operation does not suffer from stutter starts, where the fan is activated for under 5
seconds, then deactivated. Fan stutter starts can be a major source of maintenance on
the mechanical components (motors, belts, pulleys, etc.) of the fans. The Minimum Run
Timer may expire while the sensor signal is still in the alarm state.
The Minimum Run Timer is commonly confused with the Post Run Timer described in
the following paragraph.
14. Post Run Timer. Once the sensor signal falls below the alarm threshold, then the Post
Run Timer keeps the relay activated until the timer expires. The Post Run Timer
provides the benefits of the Minimum Run Timer, and additionally ensures that the
ventilation is activated long enough to ensure that the gas concentration is well below
alarm thresholds.
The Post Run Timer is commonly confused with the Minimum Run Timer previously
described.