Tips And Hints Per Bustype; As-I Bus - Fluke 125 User Manual

For Bus measurements that use input A and B (CAN,
Modbus RS-485, Profibus DP, RS-485) it is important that
the Common Mode component at the inputs is as small
as possible. This component may consist of 50 or 60 Hz
hum or other noise. Common mode signals may affect
measurement results. In case of doubt, use SCOPE
mode to investigate the waveforms at A and B. In case of
visible interference, look for a ground lead attachment
point in the system under test that shows the smallest
interference.

Tips and Hints per Bustype

AS-i Bus

The Actuator-Sensor-Interface (AS-i) is used to control
on/off devices at the factory floor. The bus consists of 2
wires marked + and – that carry a 30 Vdc supply with
superimposed data. The AS-i protocol uses continuous
polling of all devices in a fixed time schedule so that there
is continuous data traffic.
To check AS-i, ScopeMeter Channel A is on and
alternately AC coupled for data or DC coupled to test 30
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.
Connection between controller and devices is made using
a dedicated yellow flat cable as shown in the figure below
(cross section). Connection to the devices is done with
piercing connectors. To connect Probe Tip and Black
Ground Lead to + (brown conductor) and – (blue), the
TP88 Back Probe Pins (optional) can be used to probe
screw terminals at the end of the flat cable or as piercing
probes. The material of the flat cable also allows to pierce
the pin into it. After removal of the pin the material closes
again.
COM
As-i also uses M12-connectors for data as well as on/off
signals. The figure below shows where to find + and – on
on such a connector.
Appendices
Bushealth Measurements
Ch. A
A
A-3