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Advanced Diagnostics
Appendix
8.1.9
Noise
Definition
Noise is an undesired disturbance within the signal frequency band. Noise appears with differ-
ent characteristics. A high noise level causes communication problems and a lack of opera-
tional reliability. Segment noise is the maximum noise of all field device noise or the noise
measured if no field device is communicating. The field device noise is measured just before a
field device is transmitting. That does not mean that this device is causing any noise. Measure-
ment takes place to determine whether the noise value is high for a single field device only.
Often, this means that noise is caused by the device that has been transmitting right before the
device that shows the increased noise. The HD2–GT–2AD.FF.IO FF-H1 field device does not
support noise measurement per device.
Noise can have the following causes:
•
Bad wiring practice
•
Bad shielding/grounding practice
•
Supply voltage noise pulses passed onto the bus by a non-regulated power supply
•
An AC power supply injects noise into the bus
•
A regulated FOUNDATION Fieldbus power supply injects switching noise into the bus
U
A
B
Figure 8.3
A
Noise level
B
Signal level
Type
Precision
Measuring range
8.1.10
Polarity
This parameter detects the polarity of the communication signal for every field device.
8.1.11
Power Supply Voltage
This parameter indicates the voltage level of the primary and secondary bulk power.
Communication noise
t
Values
10 mV
0 ... 2.5 V, 100 Hz ... 140 kHz
147
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