Omega OM-CP-RF Series, User Manual

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OM-CP-RF Series Operations Manual
Omega Engineering, Inc. Revised 04/07/05 Page 6 of 18
3. Randomize transmit interval – If this option is selected, the transmitter will wait a
short random delay of up to 5 seconds before it transmits each data packet. This can
decrease the chances of lost packets due to devices “talking over” each other
because of long-term timer drift. Devices that are initially synchronized to transmit
10 seconds apart can drift in their timekeeping by up to 2 seconds per day, meaning
that they could potentially interfere with each other after a few days of sustained
operation. Because the transmission lasts less than a second, a random delay of up
to 5 seconds can allow the majority of the transmissions to escape interference. If
this transmitter option is not selected, the device will transmit at the interval set by
its timer to within a few milliseconds. It is then up to the user to make any necessary
accommodations for the timer drift. See “Using Multiple Devices” later in this
manual.
4. Use error correction – If this option is selected, the transmitter output format will
be modified to include a simple forward error correction scheme known as a
Hamming code. This method of error correction allows the receiver in a one-way
transmission to correct any single bit error in each block of eight data bits being
received. This option may help to increase system reliability in some environments.
Note: System reliability will most commonly be degraded by loss of signal or by burst
noise longer than a single bit, thus this option may not substantially improve
performance for the typical user. Additionally, if this option is not selected, the
device may be able to transmit two complete copies of the data packet, increasing
the likelihood that one of the copies will be received even when the other is lost due
to interference. (Each packet always contains error detection, to ensure that invalid
data is not displayed.)
Custom Transmit Interval
By default, the transmitter module will transmit a data packet with each internally
recorded data point, or if it is not recording, at the reading rate specified for the data
logger. This option allows the user to specify a custom transmit interval that will be used
only by the transmitter. Like the data logger reading rate, this interval is limited to a
minimum of 30 seconds and a maximum of 12 hours, but unlike the reading rate it may be
set to any multiple of 10 seconds. Additionally, the device can be configured to return new
data every interval, or to repeatedly send the data from the most recent internally recorded
reading. This option can be useful for the following reasons:
1. Real-time monitoring – Some applications may require relatively quick feedback of
trend data to the user, but only need to be recorded at longer intervals. With this
option, for example, an operator could check the trend of a system every 10 minutes
and make necessary adjustments to keep the system within specifications, but the
official logger record of the data only needs to indicate the value on an hourly basis.
2. Increasing system reliability – In applications where the operating environment is
unfriendly to RF, this option can be used to repeat the same data multiple times to
increase the probability of successful reception. If the logger is recording every 5
minutes, the transmitter can be configured to send the data from the last reading
every 30 seconds, allowing for 10 transmissions per logger reading. If the
environment sees a burst of RF interference a few times per minute, it is highly
probable that one or more transmissions will be received properly.