How do I tell the direct and reverse action of a gauge?

You must be referring to the positive and negative actions of PID

I don’t quite understand. By PID, do you mean the positive and negative actions? Here, PID isn’t referring to a process flow diagram, right? I’m not an instrumentation specialist either, so I don’t get it :L

Regarding control devices, we talk about positive action and negative action. Measurement instruments are categorized based on whether they have a forward output or a reverse output. For example, when 0–1 MPa corresponds to 4–20 mA, this is considered a forward output; whereas when 0–1 MPa corresponds to 20–4 mA, it is considered a reverse output

The consequence of an increase in the drive control signal is an increase in the parameter being measured; this is a positive effect. The consequence of an increasing drive control signal is a decrease in the parameter being measured; this is known as the feedback effect. After eating my fill, I swung a punch randomly; it just so happened that your lips were swollen badly – that was also a side effect.

;P, you’re really funny when you speak. Does that have anything to do with whether the control valve is air-operated for opening or closing? Since I’m not a professional in instrumentation, I don’t understand what you mean by 4-20ma and 0-20ma

If you’re not studying process control, then it’s better not to bother with it. Why worry about such things? If you really want to learn, pick up a book on process control and take a look.

I don’t seem to have seen a control valve before; I’m not familiar with it. Is the control valve open? Is it closed? Is it moving in a large amplitude? It still involves small movements; what is the amplitude of these movements? They are controlled by a signal regulated between 4 and 20 mA. So, once you understand the 4–20mA signal, does it mean the party commands the gun, right?:lol

Actuators and controllers are categorized as positive or negative acting, while other instruments are not classified in terms of positive or negative acting. When describing an actuator, one that causes the push rod to move downward as the signal pressure increases is called a direct-acting actuator ； Conversely, when the signal pressure increases, the push rod moves upward; such an actuator is called a reaction-type actuator. Structurally, positive-action and reaction-type actuators are basically identical, both consisting of a diaphragm cover, a corrugated diaphragm, a push rod component, springs, brackets, etc. By adding shims to the structure of a positive-action actuator and replacing certain components, it can be converted into a reaction-type actuator. When describing a controller: if the process variable increases, the output of the regulator also increases, which is known as positive action ； When the quantity being regulated increases, the output of the regulator decreases as a result; this is known as feedback ；

How are the positive and negative actions of a regulator defined? Answer: The positive action of a regulator generally means that the output increases as the positive deviation value increases ； The reaction of the regulator refers to a decrease in output as the positive deviation increases.