Is a DPDT signal a passive dry contact signal?
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Are 1PDT and DPDT signals passive dry contact signals?
The output signal of a two-wire transmitter is a passive signal.
Regarding 1PDT and DPDT, 1PDT refers to the number of contacts; in essence, it denotes a single-pole double-throw type with just one contact, while DPDT refers to a double-pole double-throw type. DPDT stands for double pole double throw. These two descriptions refer to different types of things, but both are used to illustrate the structural principles of relays; they do not indicate signal types. Whether it’s a dry node or a wet node depends on which power supply is being used; as for how to distinguish between dry and wet nodes, it’s recommended to search on forums – I’m too lazy to explain further.
I think with a double-throw switch, there’s no distinction between positive and negative; it should be a dry contact； Wet contacts have positive and negative poles; it’s unreasonable to create a double-pole one as well
To take the simplest example, as shown in the figure above, the DE terminal is connected to the field side as the input relay. If it is a wet node, the electricity in the DE circuit is supplied from the outside, not by the system. If it is a dead node, the electricity in the DE circuit is supplied by the system. By double-throw you mean the ABC terminals; in the diagram shown here it is indeed a double-throw relay. When the relay is activated, the BC path is active, and when it is not activated, the AB path is active. These two paths are what constitute double-throw operation.
What I’m asking is whether the output terminals ABC of this relay in your diagram are 1PDT, that is, passive dry contact signals, and not its input terminals. Additionally, the level switch connected to this relay previously outputted a collector signal, that is, it supplied voltage to the DE terminal, right? Also, my level switch power supply is 24V; then why is the collector output connection voltage set at 10–35V? Is it still okay if the voltage at the relay input terminal is 12V?
You’ve confused me; which side is the relay on? For the on-site and system sides, if the signal type on the system side is intended for the DE side. If it is a relay for on-site output, then it still depends on who supplies the power to terminals A, B, and C. It has nothing to do with your switch type.
This post was last edited by Hero Huo Yuanjia on 2017-9-18 09:10. Please take a look at the two diagrams below: the diagram showing the digital output shows the connection between my level switch and the relay. The level switch is located at the site, while the relay is in the control room. What I want to ask is whether the collector output terminals 3 and 4 of the level switch should be connected directly to terminals A1 and A2 of the relay (can the voltage generated by the collector output be used to power the relay?) ）? Should I still connect a 12V power supply between 34 A1 and A2 after that to power the relay?
Bro, help answer it, thanks
3 and 4 connected to A1 and A2 definitely require an external power supply. What’s important now is to determine where this power supply comes from. If it is provided by the system, then it’s a dry node; if it comes from an external source, for example, if you supply 220V to the instrument and then use that 220V to power this circuit, then it’s a wet node.
The instrument also has terminals 1 and 2, which are used for the 4-20mA and 24VDC power supply according to the HART protocol; terminal 3 outputs digital signals in the form of collector signals. Can this collector output voltage while simultaneously meeting the power requirements of a relay? Is it just a small switch, or does the relay require an additional power supply?