Is it in compliance with standards to connect the solenoid valve and the limit switch together via wiring?
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This post was last edited by kylestone on 2022-9-13 at 10:44. Connect the solenoid valve on the cut-off valve to the limit switch, and then use a 3x2 multi-core cable to transmit all signals to the terminals of the limit switch. One solenoid valve requires 24VDC, and the two limit switches require 24VDC dry contacts. Is this approach in compliance with the standards?
Is there a specific name or standard number for the specification?
SH/T 3019-2016 Specifications for Design of Instrument Piping and Wiring in Petrochemical Industry. 7.1.7 Signals with different voltage levels and frequency characteristics shall not share the same cable or junction box. It works fine in practice: two dry contacts and 1 wet contact, with 24V present in the circuit.
According to this specification, dry contacts and 24VDC-powered solenoid valves can be used together; both operate at a voltage level of 24V, and the current is direct current. Therefore, there’s no need to consider frequency as a parameter
According to clause 7.1.7 of the SHT3019-2016 Standard for the Design of Instrumentation and Pipeline Systems in the petrochemical industry, signals with different voltage levels and frequency characteristics should not share the same cable or the same junction box. According to clause 8.1.7 of the HGT 20512-2014 Specification for the Design of Instrument Piping and Wiring, signals of different voltage levels shall not share the same multi-core cable or wiring box. The voltage levels of instrument signals can be classified into low-voltage levels: such as thermocouple signals TC, pulse signals PC, etc ； Medium-level voltage levels: such as 4–20 mA DC signals for AI/AO, resistance temperature detector (RTD) signals, 24V DC switch signals for DI/DO, etc ； High-level voltage ranges: such as DC switch signals greater than 28V, DC control signals less than 250V, AC signals less than 28A, etc. There are four types of frequency characteristics of signals: the spectrum of power signals, the spectral density of energy signals, the power spectrum of power signals, and the energy spectral density of energy signals. The signals to which these four frequency characteristics are adapted are, respectively: periodic signals with limited power, energy signals, power signals, and energy signals. The signals from the measuring instruments we commonly use are all medium-level voltage signals; therefore, signals such as AI/AO/DI/DO/RTD can all be placed on the same main cable or in one junction box ； The DO of the electrical signal is powered by electrical supply (220V AC); it is a high-level signal. Therefore, it cannot be placed in the same cable tray as cables carrying signals from other instruments ； Other electrical signals, such as DI/AI/AO, are medium-level signals and can be placed on the same main cable.
The voltage levels of instrument signals can be categorized in the interpretation of the provisions, right?
7.1.7 The voltage levels of instrument signals can be classified into low-voltage levels: such as thermocouples, pulse signals, etc； Medium-level voltage ranges: such as 4mA–20mA DC signals, thermoresistance signals, 24V DC switch signals, etc ； High-level voltage ranges: such as DC switch signals greater than 28V, DC control signals less than 250V, AC signals less than 28A, etc. Found it~ Thank you
In actual engineering applications, DC switch signals of more than 28V do not occur; they are all 24V. So, the final conclusion is that 24VDC dry contacts and 24VDC power supply can share the same cable, right?