Test 3 wire NTK, Bosch O2 sensor signal after heat up, but, not signal. Why?

I have a 1996 Nissan Altima O2 + Catalytic converter not ready. I want make sure O2 sensor really work.

Upstream sensor (before CAT) work by measuring voltage when heated up with torch.

Downstream O2 sensor is 3 months old NTK brand. It’s direct fit, look exactly same original: 3 wire, middle black is signal, signal ground is sensor body, wht/red are heater with 6.5 om resistance. I used torch heat it up for 30 seconds – 1 mi, but no 0.9v signal voltage is detected, not even any voltage detected during heat up. I went to Pepboy bought new NTK sensor again, same result. Then, I went to Oreilly to bought Bosch direct fit O2 sensor(sensor head look different), but, it has exactly same test result.

I put sensor back on CAT, try to see if any voltage can be detected. It’s NOT wired, no car battery voltage applies to sensor. I connect voltage meter probe to middle pin, and another probe to car body. Start the car for over 10-15 min, and see the car temperature becomes normal driving condition. During the process, NO any voltage is detected. Is the test valid?

So, the 2 new O2 sensors DOES not work. Can I make such conclusion?

I am really confused.

EDIT:

I am not sure what kind of sensor it is. All I know:

1) It’s for 1996 Nissan Altima. Pepboys and Auto zone found it works for the car.

2) From all the Youtube I watched,

a) making sure heater works is to measure heater probe +/- with 6-7 om. b) It should generate voltage of max 0.9 volt when torch heated within 1 min.

3) I tested upstream O2 sensor (before CAT), and it does generated 0.9 volt. So, I assume downstream should behave the same, for same car.

BTW, I tried to test if there is resistance change between signal probe (black) and other probe (body, heater +, heater -). They are isolated. When torch heat it, no resistance change can be detected from signal and other probe: body, heater +, heater -. I am not sure if this is way to prove it’s titania-based.

Surprise, that all new O2 sensor does not work. There are must be something wrong with way to test it.