While giving Power Supply of 24 VDC to a Transmitter,why
Shield Terminal is connected either at Transmitter or at
ISB.Why not Shield Terminal connected at both ends.If the
Reason is to avoid Noise interference,which type of noice
that is interfering.Is the Noice from the 24 VDC supply
terminals or from any external source.
Answer / carl_ellis
1) A shield (screen) connected at both ends will carry
ground loop current due to the difference in ground
potentials at each end. A shield (screen) carrying current
will induce noise into the wires it is shielding.
Historically, shields (screens) have been connected at one
end only, typically at the receiver
(DCS/PLC/PAC/RTU/controller) end.
Current thinking as outlined in IEC 61000-5-2
Electromagnetic compatibility (EMC) - Part 5 Installation
and mitigation guidelines - Section 2: Earthing and cabling,
recommends grounding the shield at each
end for point-to-point and at every point for multi-drop.
Two point grounding provides protection against EMC and for
safety as well. However, this method assumes that all
points are on the same ground (i.e. use an equipotential
grounding grid).
Typically, Siemens has adopted this recommendation for
Profibus DP, an RS-485 multi-drop network. Of course, the
gotcha is "all points at the same ground potential". Not
in the real world, Mr. Siemens.
2) Although 24Vdc power supplies can be noisy, major
manufacturers produce DC power supplies with very little
ripple and excellent regulation.
DC power supplies used for HART need to meet the HART spec:
Maximum ripple (47 to 125 Hz) = 0.2V p-p
Maximum noise (500 Hz to 10 kHz) = 1.2 mV rms
Maximum series impedance (500 Hz to 10 kHz) = 10 ohm
24Vdc power supplies are not typically the source of noise
Carl Ellis
Measure First
Is This Answer Correct ? | 5 Yes | 0 No |
why relays are used with plc?
in mass flow meter what is drive friquancy ?
EXPLAIN PROPOTIONAL INTEGRAL DERIVATIVE CONTROL ACTION?
Hi, am aniket, I got engineering degree in instrumentation and control, but as their were no job availabilities for engineer's post I started working as instrumentation technician I kuwait, so my question is is this technician's experience worth for getting the position of engineer?
1 Answers Almeer Technical Services,
What is the role of P(Protional), I(Integral) and D (Derivative) in PID Controller?
please explain about actuator action? direct action & return action ?
What are the interlocks we have to check during the start up of LP/HP compressor?
what should be distance from tapping point to inallation place of instruments?
3 Answers Tasnee Petrochemicals,
I HAVE GOT TYPICAL PROBLEM WITH THE TEMP.INDICATION. THE PROBLEM IS THE K-TYPE T/COUPLE OUT PUT IS CONNECTED TO A INDICATOR.THE INDICATION FLUCTUATES SOME TIMES AND SOME TIME IT IS STABLE. WHEN I CHECKED OUT PUT OF T/COUPLE THE MV WILL NOT VARY. WHERE AS INDICATION FLUCTUATES. WHEN I GIVE MV SOURCE TO T/COUPLE EXTENSIONCABLE FROM THE FIELD IT INDICATION IS STABLE. WHEN GIVE MV SORCE TO INDICATOR ITS INDICATION IS STABLE. PLEASE CLARIFY.
I want to measure and control level in tank of size 10*5 filled with gasoline, so plz give me the solution with clear details. how to select transmitter and sensors.
We Have Two Field bus Pressure Transmitters of Different Sensor Range (I.E One is of Lower range and Another is of Higher Range).Is same Process Line. My Question is Can i provide Saturation Limit to my field Bus Transmitter as We can provide Saturation current limit to HART Instruments. As During Low Pressure Both Working OK ,But During High Pressure, transmitter with Lower sensor range Goes to Fault mode as Beyond its Sensor Limit it can Measure, So may I provide Saturation point Some where to Suppress This Fault during High Pressure.
what is basic working principle of Governer in power plant?