Wednesday, December 29, 2010
【 Weak current College 】 with digital multimeter measurement optical coupling transmission characteristics of a simplified 】
Opto coupler by light-emitting diode and transistor package. If 4N25 optocoupler, using DIP-6 package, a total of six pins, ① ② feet, respectively, Yang, cathode, ③ foot empty leg, ④, ⑤, ⑥ feet respectively transistor's e, c, b.
In the past, when using a multimeter metering coupling, only the respective test judgement of light-emitting diodes and optical transistor is good or bad, on optical coupling transmission performance does not judge. 4N25 optocoupler here to, for example, the introduction of a new transmission characteristics measuring optical coupling.
1. determine the light-emitting diodes is good or bad and polarity: multimeter R×1k retaining measurement diodes of positive and negative to positive resistance, General resistance to dozens thousand euro, thousand euro should normally reverse resistance to ∞. The measured resistance small, then red is the diode anode.
2. a judgment by optical transistor is good or bad and magnification: will switch from electric barrier multimeter to transistor NPN hFE block, use the E-outlet hole connection ④ feet emitter, C hole connection ⑤ feet set electrode, the B hole connection ⑥ foot base, displays the value of the current magnification triode. General optical coupling hFE value is 100 to several hundred, if the displayed value is zero or overflow to ∞, transistor circuit or open circuit, is corrupted.
3. optical coupling transmission characteristic of the measurement: test specific connection see the following figure, the digital multimeter switch dial to shift a diode, black pen received emitter, red pen pick set electrode, ⑥ foot base electrode dangling. Now, voltage reference in the table by table diode 2.8V retaining the measuring circuit, added to the transistor of c, e-knot range. But because input diode end-no optical signals and not via the LCD display overflow symbols. When input ② feet insert E hole, ① feet insert C hole NPN socket, base power within a table by table 2.8V transistor hFE retaining the measuring circuit, so that the light-emitting diode lighting, light for illumination and conduction of the transistor, the displayed value by overflow symbols instantly to 188 of the indication. ① When fractured foot anode and C hole intersected, display value indication from 188 instantly returned to overflow symbols. Different optical coupling, transmission properties and efficiency are not the same, you can choose a smaller font, the indication displayed value stability not beating optical coupling applications.
Because the table use 9V battery, to input diode power on time is not too long, so as not to reduce the battery life and measuring accuracy can be intermittent contact method.