Allen-Bradley MediaChecker 1788-MCHKR Manual page 22

22
The Test Function (TEST)
Display
1. The MediaChecker measures lengths to 650 m; however distances in feet beyond 999 ft are rounded to the nearest 10 ft.
2. A short greater than zero ohms causes the MediaChecker to display a length greater than the actual distance to the short. Figure 4
on page 23 illustrates this process using an Ethernet example. The MediaChecker uses ohms/foot to calculate distance to a short.
1788-UM002A-US-P – April 2000
Table 10. ControlNet Test Failures
Failure
The MediaChecker detects a cable length
greater than 2130 ft (650 m)
maximum it can measure.
The MediaChecker detects a resistance that
is greater than the resistance of 2130 ft
1 of cable (about 65 Ω).
(650 m)
The MediaChecker detects a resistance that
is less than the resistance of 2130 ft (650 m)
of cable (about 65 Ω). 2
If "2130'" (650 m)
1
, which is the longer than the maximum the
MediaChecker can measure. Break the
cable near its center and measure the two
parts separately.
A terminator resistor is probably connected
to one end of the bus. Remove the
terminator; then retest.
Or, subtract the terminator's resistance
(75 Ω) from the measured resistance to get
the cable resistance. Then use the
procedure under "Calculating the Distance
to a Short" on page 32 to calculate the
cable length.
"SHORT" is blinking. A resistance less than
1
65 Ω (which is too low to be a terminator) is
across the line.
The display shows the most likely distance
to the fault.
Description
1
is flashing, the cable is