Modbus Iea-485/Rs-485; Foundation Fieldbus H1 31.25 Kbits/S - Fluke 125 User Manual

they can be measured as well as far as V-Levels are
concerned.
Tx: Connect to Ch. A
Rx: Connect to Ch. A
CONTROLLER
Signal Ground: to COM
MOD-RS-232

Modbus IEA-485/RS-485

Is in use in Process Industry, Building and Factory
Automation. Modbus System layout is shown in the figure
below. Continuous Data traffic is not ensured. To check
this type of bus, ScopeMeter Channel A and B are on and
DC coupled. The recommended probes are STL120 (1:1).
Probe tip A must be attached to the + (positive) wire;
Probe tip B to the – (negative) wire, and the COM input
(or Black Ground Lead) to Signal Ground (GND).
+
-
CONTROLLER DEVICE 1
Gnd.
DEVICE UNDER
CONTROL
DEVICE 2
Connect to Ch. A
Connect to Ch. B
Connect to COM

Foundation Fieldbus H1 31.25 kBits/s

Is used to control 'field equipment' such as sensors,
actuators, valves, and I/O devices via a two-wire
connection. The system allows two-way communication
between controller and the devices. Data traffic is
continuous. The wires are marked + and – and carry a
DC supply of about 24 Vdc with superimposed data of
about 800 mVpp. The figure below shows the bus
structure.
To check Foundation Fieldbus, ScopeMeter Channel A is
on and alternately AC coupled for data or DC coupled to
test 24 Vdc. The recommended probe is STL120 (1:1).
The probe tip must be connected to the + (positive) wire;
the COM input (or Black Ground Lead) to the – (negative)
wire. Suitable measuring spots are the screw terminals
that are present in a system's junction boxes. If preferred,
you can use the TP88 Back Probe Pins (optional) to
probe these terminals at the wire entry point. Commonly
used wire colors are orange for + and blue for –.
Appendices
Bushealth Measurements
A
A-7