How to judge the quality of optocouplers?

Using a DC5V power supply, attenuate through a resistor, press a button, connect one end of the optocoupler input, and the other end is grounded. The output end of the optocoupler is connected to+5V through an pull-up resistor, and the other end is connected to an LED display. The LED - ground is sufficient.
Detection:
1. Remove the suspected faulty optocoupler using the comparison method, measure the forward and reverse resistance values of its internal diode and transistor using a multimeter, and compare it with the measured values of the corresponding pins of a good optocoupler. If the resistance difference is significant, it indicates that the optocoupler is damaged.
2. The following is an example of using EL817 optocoupler detection to illustrate the method of digital multimeter detection. When testing, insert the+terminal {1} and - terminal {2} pins of the optocoupler diode into the C and E sockets of the Hfe of the digital multimeter, respectively. At this time, the digital multimeter should be placed in the NPN position; Then connect the C-pole {5} of the optocoupler to the black probe of the pointer type multimeter, and connect the e-pole {4} to the red probe. Set the pointer type multimeter to the RX1k position.
This way, the condition of the optocoupler can be determined by the deflection angle of the pointer on the pointer type multimeter, which is actually the change in photocurrent. The greater the deflection angle of the pointer to the right, the higher the photoelectric conversion efficiency of the optocoupler, that is, the higher the transmission ratio, and vice versa; If the watch needle does not move, it indicates that the optocoupler is damaged.
3. The photoelectric effect judgment method still takes the detection of EL817 optocoupler as an example, and the detection circuit is shown in Figure 2. Place the multimeter in the RX1k resistance range, and connect the two probes to the output terminals {4} and {5} of the optocoupler, respectively; Then, connect a 1.5V battery in series with a resistance of 50-100 Ω. Connect the positive end of the battery to the {1} pin of EL817, the negative end to the {2} pin, or the positive end to the {1} pin and the negative end to the {2} pin. Observe the pointer deflection of the multimeter connected to the output end.
If the pointer swings, it indicates that the optocoupler is good. If it does not swing, it indicates that the optocoupler is damaged. The larger the deflection angle of the multimeter pointer swing, the higher the photoelectric conversion sensitivity.