Analog and Digital Wires in Same Raceway
Analog and Digital Wires in Same Raceway
(OP)
I have a situation wherein I have cabinet with existing wireways. I do not have any space to provide another wireway. We ahve installed existing instrument amplifiers with both 24VDC digital and 4~20mA Analog output terminals. Unfortunately we could not physically separate both signal wires due to space limitations. This wireway is just beside the instrument amplifiers.
If the Analog wires are operated at 4~20mA, 24VDC and the digital signals are operated at 24VDC and the insulation voltages for the two set of signal wires are 300V and 600V respectively, is it technically acceptable to combine them in one wireway?
By the way, this particular wireway is the one beside the instrument amplifiers and routed to a point where it terminates to two separate analog and digital wireways inside the cabinet.
If the Analog wires are operated at 4~20mA, 24VDC and the digital signals are operated at 24VDC and the insulation voltages for the two set of signal wires are 300V and 600V respectively, is it technically acceptable to combine them in one wireway?
By the way, this particular wireway is the one beside the instrument amplifiers and routed to a point where it terminates to two separate analog and digital wireways inside the cabinet.
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata






RE: Analog and Digital Wires in Same Raceway
It is technically lame.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Analog and Digital Wires in Same Raceway
RE: Analog and Digital Wires in Same Raceway
Oilfield and power plants have different specifications and I always followed their specs at their plants but I never had a problem when they were combined at other facilities. If you look at the input impedance of a typical 24VDC Input module, the 4-20mA is probably drawing more current and usually it is biased at 24VDC.
RE: Analog and Digital Wires in Same Raceway
Without hyjacking the post, we did experience signal distortions when an additional UHF amplifier was inadvertently installed inside the interface cabinet! 4-20mA signals went muddled everytime UHF signals come.
RE: Analog and Digital Wires in Same Raceway
As long as the 24 V DC isn't PWM controlled with a high carrier frequency and the analogue signals are not mV signals and your wires are not more than 5 - 10 meters (15 - 30 feet), you will be fine.
Inductive loads on the 24 V side shall, of course, always have snubbers or diodes and sometimes it is a good idea to include a current limiting resistor if you have high wattage incandescent lamps. The coldstart current will sometimes be so high that it can disturb analogue signals. But that is very rare.
VFD motor cables and HF/UHF signals are the bad guys. They sometimes influence your analogue signals also when routed in different wireways. And shielded.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Analog and Digital Wires in Same Raceway
GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata