Voltage
Communication
State Meaning Acceptable Range
1
Bit Voltage Active + or – with respect
to COM when
communication is
occurring.
+2.0 to +4.0 VDC (+ to
Com), -2.0 to -4.0 VDC (- to
Com). When comparing the
absolute value of these two
readings, there should be
no more than
approximately a 0.2 VDC
difference.
Differential
Voltage, Total
Voltage
Active The + to COM
Reading plus the
absolute value of
the - to COM
Reading when
communication is
occurring.
2.5VDC to 8VDC is
acceptable.
1
These voltages should typically not be read with a Volt-Ohm-Meter (VOM). Use the
FIT instead. Idle bus voltages are read with a VOM when communication is not
occurring. When FIT is connected to a bus and then powered on, it will display
Offline if the bus is Idle.
Tips for Correcting Bus Installation Problems
The MS/TP Bus is subject to a number of installation factors that can affect
performance. Consider the following common physical attributes when trying to
resolve communication problems:
Validate controller/device power is available and undisrupted.
Check wiring for:
- Proper wire gauge, cable type, connections, polarity, and lengths.
- Opens and shorts.
- Confirmation that one shield ground point exists per bus segment
(made at the source of the bus segment —the NAE, Side B of a Repeater).
Check EOLs to verify that EOL terminations are only at the ends of daisy chains
for each bus segment.
Check addresses for:
- duplicate addresses
- address ranges are sequential
Check for and eliminate T-Taps (wire configurations that create a T shape) and
star configurations.
Check for consistent baud rates (often baud rates problems occur with vendor
devices and repeaters).
Check for sources of electrical interference.
To Next Page
Loading...
Need help?
General