Problems with four-wire transmitters

For the system, this is an active signal; the system card does not need to be powered anymore. Personal opinion

Yes. No problem. But many people don’t understand it. That’s why foreigners never talk about something having a source or not; they just refer to it in terms of the number of wires. Clear and understood. Some refurbishment shops like to come up with these ridiculous things to trick people.

It is active, but some four-wire systems use a two-wire connection method; it depends on how the transmitter is designed

For the system, the signal output by a four-wire instrument is an active signal. Passive signals and active signals 1. Definitions of passive signals and active signals: For current signals, if a device has its own separate power supply line, then the signal output it provides (such as 4-20mA) is considered an active signal ； If the device does not have its own independent power supply, the signal it provides is a passive signal. The output signals of three-wire and four-wire instruments are active signals, while the output of two-wire instruments is a passive signal. Active signals: yunrun.com.cn/tech/1634.html. 2. How to acquire passive and active signals: ① For acquiring active signals, it’s simple – first, turn on the power supply of the signal source device (there are usually two types: three-wire and four-wire systems) to enable the device to operate properly; then, connect the positive and negative terminals of the input interface of the acquisition device to the corresponding positive and negative terminals of the signal source device. ②For the acquisition of passive signals, a DC 24V power supply is required first (since two-wire instruments that generate passive signals do not have an independent power source; when they need to output a 4-20mA signal, their operating voltage must be provided by an external device). This DC24V power supply can be an independent power source, or it can provide the power supply function for passive signal acquisition devices ； Secondly, a proper circuit must be formed among the two-wire instrument, the DC24V power supply, and the passive signal acquisition device: the positive terminal of the DC24V power supply is connected to the positive terminal of the 4-20mA output of the two-wire instrument; the negative terminal of the 4-20mA output from the two-wire instrument is connected to the positive terminal of the 4-20mA signal input terminal of the acquisition device; and the negative terminal of the 4-20mA signal input terminal of the acquisition device is connected to the negative terminal of the DC24V power supply. This creates a complete circuit.

For the card modules, just change the DIP switches; some of them don’t require a 24V power supply.

This post was last edited by leit on 2019-1-9 at 11:49. It’s not at all the case; active and passive are relative concepts. What does it have to do with foreign or domestic matters? It is a four-wire signal. From the perspective of the DCS, as viewed in the direction from the DCS to the instrument, this signal can operate without the need for separate power supply for cards or safety barriers; it has its own power source, making it an active signal. But looking from the table toward the DCS direction, it’s exactly the opposite.

There’s an interesting thing: a new set of equipment was installed, using a certain foreign DCS system. Engineers from the manufacturer came to carry out adjustments. They were expert in the system, but only had a basic understanding of the actual installation site. I assisted them in checking the wiring and making adjustments. During each communication session, we can discuss other issues very smoothly, but it’s always the case that regarding active signals and passive signals, what I say is the opposite of what he says. Later, the two of them sat down and discussed it in detail, and then realized that neither of them was wrong. He works in systems, so he always views things from a systems perspective, while I work on-site; I habitually look at the systems from the on-site perspective.

This post was last edited by 49205455 on 2019-1-9 at 13:25. Do you know what I mean? It’s not at all. A four-wire system could clearly solve all the problems. Why bother with active and passive ones? In this country, people like to talk about seniority and act as if they’re very knowledgeable; it’s people like you who think they know a lot and take advantage of newcomers. In reality, all they know is nonsense. Then they can even come up with sets of theories. In actual work, it turns out to be nothing but theory on paper, with tons of mistakes.

This post was last edited by 49205455 on 2019-1-9 at 13:28. No one is to blame; words are easier to say than actions. You are the client – how dare Party B say you’re wrong? What does it matter to you whether you’re right or wrong? He just needs to get the job done and receive his payment; it’s none of your business whether you’re right or wrong. On the surface, he says he’s fine with you and everything. But inside, I was thinking: This idiot. Whether it’s active or passive, this term has been used by DCS from the very beginning, and there is only one way of referring to it. There is no such thing as relativity at all. Still dealing with relativity? Can’t your watch work without a power source? All components at the field side are active.

This post was last edited by leit on 1/9/2019 at 14:46. You discuss issues here while looking down on domestic entities and dismissing Party B whenever there’s a problem. Different opinions are possible; maybe I’m 100% wrong, but is it useful to attack people personally? As the saying goes, one gets caught in something or other. There’s no way to go back; I just accept my bad luck!