How are the current transfer ratio (CTR), trigger LED current, and threshold input current measured?

Measurement procedure for current transfer ratio, IC/IF (CTR) - Transistor output

Refer to Toshiba Application Note “Glossary of Photocoupler and Photorelay Terms”, section 2. Measurement procedure for current transfer ratio, IC/IF(CTR) - Transistor output, section 3. Measurement procedure for threshold input current, IFHL(IFLH) - IC output, and section 4. Measurement procedure for trigger LED current, IFT.
(https://toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/application-note.html)

Example: Current transfer ratio (CTR) measurement circuit
(Excerpts from Application Note "Glossary of Photocoupler and Photorelay Terms",
section 2. Measurement procedure for current transfer ratio,IC/IF(CTR)- Transistor output)

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