Communication methods for thermal resistors, thermocouples, and pressure transmitters in factory production sites
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In factory production environments, from thermal resistors, thermocouples, pressure transmitters, and temperature transmitters to the IO cards in the control room, what communication method is generally used? Is it RS485? Why do some people say it’s parallel communication?
Thermal resistor – Resistance signal input card； Thermocouple – millivolt signal input card ； Pressure transmitters, temperature transmitters – 4~20mA signal input card, with the option to add HART protocol communication. RS485 is used for communication between systems.
Transmitters generally use 4-20mA communication. For thermal resistors and thermocouples, if no temperature transmitter is installed on-site, thermal resistors transmit resistance signals, while thermocouples transmit potential (millivolt) signals to the card module
Don’t resistance signals, millivolt signals, and 4–20mA signals fall under RS485 communication? What does system refer to?
Instrument resistance signals, millivolt signals, and 4–20mA signals are all output signals from instruments and sensors; they are something different from communication.
Communication generally refers to digital signals, such as 010101, while a protocol is the set of rules for interpreting strings.
Communication occurs only when the instrument’s output signal is digital. . . Communication refers to the interaction between the instrument side and the signal acquisition side, including inquiry, response, handshake, decoding, as well as the exchange of digital measurement data. When the instrument’s output signals are voltage, current, or frequency, the electrical signal is simply transmitted by the instrument actively, while the signal acquisition unit merely acts to collect the signals. . . There is no back-and-forth \"communication\" between the two parties. . .
That’s a good way of putting it; communication exists only when there is back-and-forth between both parties.
This kind of question-and-answer exchange is what constitutes communication. What are some specific examples?
Think about the hand controller. After the connection is established, first, the handheld controller asks for certain data, and the instrument responds with those data. . . If not asked, no answer; if asked frequently, an answer is given. Secondly, the handheld controller can be used to modify instrument parameters – the controller sends a command to make changes, and the instrument responds with \"Execute\" before making the adjustments. With the modification, the handheld controller can send query commands again, and the instrument should respond by uploading the updated data. .