Calibration
Page 194 OmniTrax Product Guide
Mutual interference
Mutual interference is the term used to describe the RF interference that is inherent when two
transmitter receiver pairs operate in close proximity at the same time and frequency. In most
cases, mutual interference is not a problem for the OmniTrax system. Following the recommended
installation procedures and setting up the processor synchronization prevents mutual interference
from disrupting operation. However, there are a number of environmental factors including the
installation medium (e.g., light sandy soil types, concrete and asphalt) as well as variances in
cable depth and spacing, that can lead to an increased effect from mutual interference. In a worst
case scenario, mutual interference can cause false alarms, thereby affecting the overall
confidence in the system.
To prevent mutual interference from affecting operation, there are two UCM settings for the RF
transmitter on each cable side (A-side and B-side) - Duty Cycle and Coding.
Transmitter Duty Cycle:
Duty Cycle refers to the time period that the OmniTrax RF transmitter is ON and OFF. There are
two Duty Cycle settings, 100% in which the transmitter is always ON, and 50% in which the
transmitter is ON for 25 ms then OFF for 25 ms in a repeating pattern. All single processor
systems should use the 100% Duty Cycle setting. Network systems should use the 50% Duty
Cycle setting.
Mutual interference can be recognized on a UCM plot as noise spikes moving along the range
axis. If the amplitude of the noise spikes exceeds the cable margin, false alarms will occur. To
prevent mutual interference between OmniTrax processors set the Duty Cycle for the affected
processors to 50%. The Duty Cycle must be set independently for each cable side (A-side and
B-side). In addition, specify the Coding as outlined in the following section.
The Duty Cycle can also be used to determine if there is an outside source of RF interference that
is affecting system operation. If a site is experiencing false alarms that appear to result from RF
interference, and changing the Duty Cycle and Coding settings do not correct the problem, then
there is most likely an outside source of RF interference. In this case you must locate and correct
the source of the interference.
Transmitter Coding
Coding is used with the Duty Cycle setting to prevent mutual interference between OmniTrax
processors. Coding sets the time slot for the 50% Duty Cycle transmission. For the A-side 1 is
the first transmission time slot and 2 is the second. For the B-side 1 is the first transmission time
slot and 2 is the second. At 100% Duty Cycle, Coding defaults to 1 + 2 for the A-side and
1 + 2 for the B-side (transmitter is always ON).
When selecting a 50% Duty Cycle you use the Coding to set the time slots for the connected cable
sets so that the two transmitters are not ON at the same time. For example, the A-side cable for
processor 1 is set to 1. The B-side cable from processor 2, which is connected to the A-side
cable from processor 1, is set to 2. Therefore, when the A-side transmitter for processor 1 is ON,
the B-side transmitter for processor 2 is OFF, and vice-versa.
Note Sensor cable sets that have less than 30 m (98 ft.) of parallel separation
or 45 m (148 ft.) of perpendicular separation (end to end) must use a
50% duty cycle and alternate coding (e.g., 1 and 2).
To Next Page
Loading...
