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 8 of 18
restarted. If the application only requires the wireless transmitter without data logging
capability, the device may be stopped immediately (when the “Transmit only while logging”
option is not selected) after launching without affecting the scheduled start of the wireless
transmissions. This will marginally improve the battery life when data logging capability is
not required.
If immediate start is specified, the device will begin logging immediately, but it will
inhibit transmitter output for the first reading to comply with FCC regulations. To ensure the
first transmission is sent, use the delayed start mode with a 1-2 minute delay (minimum
allowed by software).
USING MULTIPLE DEVICES
When using more than one RF transmitter, should transmissions overlap, it is certain
that one or both of the transmissions will be lost. There are several methods, described
below in order of complexity (least to most), to circumvent this issue:
1. Rely on the logged data - The OM-CP-RF transmitters can be configured to log all
data to non-volatile memory. If a data point is lost, it may be fully recovered by a
later off-load.
2. Provide a direct connection - If it is possible to have a PC always connected to the
OM-CP-RF series logger (while monitoring via RF elsewhere), then using the serial
output transmitter mode or the real-time chart recording feature of the software will
avoid RF interference.
3. Randomize the transmission interval – This option is selected from the wireless
configuration menu. Selecting this option will cause the transmitter to wait a short
random delay of up to 5 seconds before it transmits each data packet. Should two
transmitters drift to within 5 seconds of each other, this feature will reduce the
dropped points by about 80% until the transmitter clocks drift apart again. This will
also decrease the chances of sequential lost packets.
4. Staggering of scheduled transmissions – By starting the OM-CP-RF transmitters
at different times, the transmissions will not overlap until the time drift between the
transmitter clocks causes transmission collisions. At room temperature, the typical
clock will drift no more than 1-2 seconds per day. Higher or lower temperatures will
cause more drift. For example: if you use delay start to start one transmitter at
11:00:00 and a second transmitter at 11:00:30 (at 1 minute sample rates), then
typically they would run for about 30 days (at similar temperatures) before there
was a possibility of a collision. However, temperature fluctuations that deviate up or
down from room temperature will generally cause the clock to run slower. Thus,
potential collisions depend the time between samples, relative clock accuracy and
relative ambient temperatures.
5. Prime number scheduled transmissions – This method utilizes prime numbers to
help prevent transmission collisions. See the next section for further detail on this
method.