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changes 5mm from the last report. The distance increase and decrease are unsigned
values with units in millimeters.
Periodic reporting and hold time are described in the sections below.
7.3.3.
Hold Time
The purpose of the hold time is to add “debounce” or “hysteresis” to the sensor so that
it does not send rapid events when the measurements are sitting close to the threshold.
The measurements for the ultrasonic may jump between multiple values if it is not
mounted properly, and thus if the measurement continuously jumps above and below a
threshold, it will send a flood of threshold events without any hold time defined. For
example, if the lower threshold for the ultrasonic is set to 1000 (1 meter) and the
distance measurements are bouncing between say 900 and 1100 every 1 second, then
there will be a lower threshold event every 2 seconds. If a hold time of 10 seconds is
defined, no threshold events occur. The measurement must then drop below 1000 and
stay below that threshold for 10 seconds before a lower threshold event message is
created.
The hold time is defined in 1 minute increments when the most significant bit is 0, and it
is defined in 1 second increments when the most significant bit is 1 as shown in the
following table.
Table 10 Period Bye (byte 2) from Downlink Configuration Message
Bit 7
Bits 6:0
0
Hold time defined in minutes (1-127 minutes)
1
Hold time defined in seconds (1-127 seconds)
For example, to set a hold time of 4 minutes, byte 2 would be set to 0x04. To set the
hold time to 15 seconds, byte 2 would be set to 0x8f.
It is highly recommended to use hold times in order to prevent spurious
events and unnecessary messages.
