Which instruments specifically fall under analog and digital signals?

Among automated instruments, which ones are digital, and which ones are analog? Please ask the teacher to inform me

4-20mA, 0-10V, and so on all belong to analog signals. On this topic, it is recommended to first consult the basic books on instruments~

Common ones include digital switches, valve monitoring, level switches, and various alarm signals. For example, proximity switches. Of course, many transmitters can output both analog and digital signals. Common analog signals include various transmitters, such as those for pressure, temperature, flow, and so on

Analog signals are generally used in transmitters and control valves. There are two types: one is to input analog values into the system, such as transmitters. Expressed with AI. Generally, it is 1~5V and 4~20mA. Small numbers correspond to the lower limit, while large numbers correspond to the upper limit. For example, if the range of a pressure transmitter is 0–10 MPa, then the AI signal it sends to the system is 4 mA, indicating that the current pressure is 0 MPa; 20 mA indicates that the current pressure is 10 MPa. The value in the middle corresponds to the current (which is linearly related to voltage); another type is the signal that the system outputs to the field devices, denoted as AO. Common ones include valves, frequency converters, and so on. The correspondence is consistent with the AI signals. 1~5V and 4~20mA correspond to 0~100% or 0~50HZ. Digital signals are generally used for valve control and status feedback. There are also two types: the system sends a signal to devices such as solenoid valves (relays), which is a digital output, denoted as DO. An energized solenoid valve (relay engaged) is indicated by 1. Conversely, using a device such as a limit switch to send a signal to the system constitutes digital input. Denoted by DI. A closed field contact is indicated by 1, while an open one is indicated by 0.

The simple difference is that a continuously varying value is an analog quantity, while one that has only two states—on and off, or high and low—is a digital quantity.

Analog values are those that change continuously, such as 4-20mA, 0-10V, etc.; these include parameters like pressure, temperature, and flow rate. Digital values, on the other hand, have only two states: on/off or high/low. Examples of digital values include valve status, level switches, and various alarm signals.

I want to answer, but I feel that what I say isn’t as detailed as what’s on the fifth floor :P:P

Low-voltage signals are basically analog signals, milliampere signals, and digital signals. Alternating current and direct current, on the other hand, are digital signals – they are either powered on or powered off

The 4-20mA and 1-5V signals, as well as the frequency signals transmitted by field instruments, along with the millivolt and resistance value signals from thermocouples and thermal resistors, are all analog signals. Digital signals mainly include on/off signals from system outputs, on/off position signals from on-site feedback, and signals indicating whether the equipment is running or stopped.

Analog quantity: Simply put, it is a quantity that changes continuously, such as a current signal. Digital quantity: In simple terms, it refers to a quantity that changes discontinuously, such as 1 and 0 in computers.