How do active signal isolators connect to active signals

If the instrument panel person in the mechanical automation work is not clear about the passive signal, the active signal, the passive contact (dry contact), the active contact (wet contact), it must be confused.

(A) passive signal and active signal (analog input)

(1) Define passive signal and active signal

For the current flow signal, if the machine has a separate working power plug, the signal output it shows (such as 4-50mA) is an active signal; If the machine itself does not have a switching power supply in separate operation, the signal it presents is a passive signal. The output signal of the three-wire instrument panel and four-wire signal isolator is the active signal, and the output of the two-wire signal isolator is the passive signal.

(2) How to collect passive signals and active signals

① For the collection of active signals is very simple, first of all to access the switching power supply of the signal source machine equipment (generally there are three wire system and four wire system two) so that the machine equipment all work normally, followed by the collection machine equipment input jack of the positive end and the negative end of the positive and negative end of the signal source machine equipment matching the connection line.

(2) For the collection of passive signals, an AC 24V switching power supply is required first (because the two-wire instrument panel with passive signals does not have a separate working switching power supply, when it must output 4-50mA signals, its working standard voltage must be shown by peripheral devices. The DC24V switching power supply can be an external power supply, but also passive signal collection machine equipment distribution equipment function show); Second, the two-wire instrument panel, DC24V switching power supply and passive signal collection machine equipment among the three should produce the appropriate control loop: The positive stage of the DC24V switching power supply is connected to the positive stage of the 4-50mA output of the two-wire instrument panel, the negative stage of the 4-50mA output of the two-wire instrument panel is connected to the 4-50mA signal input of the collection machine and equipment, and the negative stage of the 4-50mA signal input of the collection machine and equipment is connected to the negative stage of the DC24V switching power supply, so as to generate a detailed control loop.

(2) Active contact and passive contact (switching quantity)

(1) Definition of passive contact

Passive contact alias dry contact or passive power switch, dry contact is an electrical switch, with two cases of closing and breaking; There is no optical activity between the two contacts and they can be exchanged.

(2) Universal passive contact signal

① A variety of power switches such as: stroke switch, limit switch, button switch, transfer switch, temperature switch, float level meter, etc.; ② A variety of function keys;

(3) The output of various sensors, such as: sensors in the natural environment driving force supervision: water sensor, fire alarm system sensor, glass breakage, vibration, smoke and solidification sensor; Automobile relay, reed tube output.

(3) The definition of active contact

Active contact alias wet contact or active power switch, with power and no power two cases; There is optical activity in the middle of the two contacts, which can not be reversed.

(4) Universal active contact signal

① Put the dry contact signal above, connect the switching power supply, and then use the other one * of the switching power supply as the output, which is the active connection point signal. The common wet working voltage range on industrial control systems is DC0-30V, and the standard is DC24V; The general wet working voltage range in the secondary circuit of electrical equipment is AC110-220V, and the common AC380V or AC220V wet contact is AC380V.

It is also possible to use TTL level output as a wet contact; In general, the TTL level must have a cache output, such as: 7407, 245, 244, etc., and VCC to form a control loop; 244, 245 can also form a control loop with gnd; Can drive distant photocouplers.

③ Collector junction output and VCC of NPN triple * tube.

④ Darlington tube collector output and VCC.

⑤ Infrared reflector sensor and infrared reflector sensor output.

(5) Advantages of passive contact

In the application of industrial control systems, due to the non-optical activity limit of passive contacts (dry contacts), the total number of passive contacts far exceeds that of active contacts, and passive contacts have the following advantages:

① Free connection, reduce engineering costs and project staff regulations, improve the speed of the project.

② Solve the total number of dry contact switches.

(3) Even if the long-term short-circuit failure of the power line connected to the dry contact is not easy to destroy the local control system, it will not destroy the distant machinery and equipment.

④ The connection is very easy, and the jack is very easy to unify.