Solution that worked for me:
A) Test which PDs is the problem (suggested by @CamDavidsonPilon)
This will remove the REF signal from the calculation and you’ll see both signals in the chart. This way, we can see how both signals look and figure out which PD is causing problems.
1 . Set both channels to 90 in config.ini
[od_config.photodiode_channel]
1=90
2=90
2 . Create a test experiment and start OD readings (you should see plots similar at the right side of the picture below)
B) Replace the malfunctioning PD
1 . Replace all the PDs that were giving “0” measurement in the OD plot with
2 . Create a test experiment and start OD readings.
For example, in the picture above channel 2 (ch2 aka 90) were giving “0”. Hence, these PDs were replaced with new PDs. After this, check the channel 2 (ch2 aka 90) readings.
Today, the same also happened with a worker in another cluster. I replaced the PDs with new ones + changed the “ir_intensity=auto” (it was ir_intensity=70) and this fixed the problem.
Personal experience: Even for “near perfectly clear” media, the sensors always generate some voltage (i.e., the reading is never just “0”, it is always ~0.000X). At least in all my experiments, Piroeactors that showed “0” in the readings never recovered or scaled in OD reading even when the culture became turbid. However, if it was even 0.0001, I observed the OD readings to scale with the media turbidity. So my take on this is that:
- The PDs getting worn out, most likely, due to being old.
- There is a loss in connection between the PDs and the HAT port (less likely as this does not seem to be happening with channel 1 and channel A)