Relay power supply
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Ask for help: Under what circumstances does a relay need to be powered?
1. When the power supply of the solenoid valve is 24VDC, the DO card in the DCS system outputs to the relay, and the relay outputs an active (24VDC) signal to the solenoid valve. The action of the solenoid valve is interlocked. At this time, the power supply of the solenoid valve is provided by the relay.； 2. When the power supply of the solenoid valve is 220VDC, the DO card in the DCS system outputs to the relay, and the relay outputs a passive (24VDC) signal to the solenoid valve, and the solenoid valve action is interlocked. At this time, the power supply for the solenoid valve is also provided by the power supply box or power distribution cabinet. ；
Isolate or use small voltage to control large voltage. The work unit has a lubrication station, and its own cabinet contains a set of things, such as relays and contactors. For example, let’s take the control of the high-pressure pump motor in the lubrication station.: The relay in the PLC cabinet, 24V coil -> 220V contact, and then the 220V coil -> 220V contact in the cabinet next to the machine, the contact is connected in series to the contactor coil of the pump motor. In this way, a high-voltage pump uses two intermediate relays.
1. When digital input enters PLC or DCS, an intermediate relay is used for isolation. 2. Digital output uses relays to control large contact equipment from small contacts. This post was last edited by faner on 2009-3-18 15:17 ]
I’m not quite sure about the purpose of the question, and I feel like some of the answers are wrong: lol I’ll try to answer them.； It is considered necessary to add relays in three cases: 1. The load is large and the relay contact output energy is not enough. It is necessary to increase the relay contact output with high current. ； 2. Different voltage and current levels require intermediate relays for matching. ； For example, if the contact is 3AAC and the load is 3ADC, it cannot be used. Note: For the same voltage and current level, DC can drive AC, but AC cannot drive DC. 3. Need to add auxiliary contacts (the number of original relay output contacts is not enough) or need to be expanded (normally open to normally closed, normally closed to normally open).
The so-called relay power supply by the poster should be to control the on-and-off situation of the live wire or neutral wire of the on-site electrical equipment through the relay. Generally, this power supply method is required for solenoid valves, etc., or to control the on-off of DC 220 live wire supplied to the pump by electrical appliances, etc., which is what we call wet node.
Wet node, I haven’t heard of it, what about others?