Incorrect PMT reading

[ouraniamge@gmail.com]

I am attempting to read the signal from a Newport 77348 photomultiplier tube. It is connected to a BNC 2110 terminal block which is connected to a PXIe 1073 that then goes to my PC where I have some code to read the input voltage. The PMT seems to work when connected to an oscilloscope (gives a reasonable response when light is shine on it) and the DAQ setup has successfully read off of a photodiode in the past. The issue arises when the PMT's output is fed directly into the DAQ card. When the bias voltage is applied, the DAQ reads a constant -10.2 volts. I wonder if it is an impedance matching issue, but I can't seem to find much information on the input impedance fo the PXIe 1073.

We've also tried routing the PMT through a gated photon counter and a Lock-in amplifier (separately), and that seems to provide some non-static reading. However, we'd like to, if possible, just read the voltage out directly from the PMT, since there are other issues regarding sampling rates with the photon counter and the Lock-in.

Thanks in advance.

[santo_13]

FYI - PXIe 1073 is a chassis and not an instrument. What exact instrument do you connect it to?

Please share full information about the bias voltage, how exactly you wired everything up, what settings you used in the DAQ when configuring the AI, etc.

[AnalogKid2DigitalMan]

Can you supply a schematic for all connections made to the PMT including the DAQ card connections?

EDIT: Just saw Santhosh requested that and additional relevant details.

-AK2DM 

[ouraniamge@gmail.com]

Hello, thank you for replying! We typically use a bias of 600-800 volts on the PMT (power supply is an SRS PS325 if that's helpful at all). We're trying to wire the PMT to the BNC 2110 with what I assume is a 50 ohm coax into one of the analog inputs. The BNC 2110 is connected to the chassis, there's a crude schematic attached.

I've been using floating source for the measurement and a differential terminal configuration. I can't seem to use any configuration besides that. I've just been reading the voltage using an express task (10 to -10 V signal range, continuous sampling at a rate of 1k Hz). Let me know if there's any other information I need to provide.

Also apologies if I relay things imprecisely, I'm a first year undergraduate and I don't have a lot of hands on lab experience 😅. Thank you again!

[AnalogKid2DigitalMan · Accepted solution]

If the PMT is expecting 50 ohm termination then you probably have an impedance mismatch feeding it directly to the high input impedance of the DAQ card.

Try putting a 50 ohm resistor across the analog input terminals of the DAQ.

-AK2DM

[Henrik_Volkers · Accepted solution]

A 50 Ohm feedthrough or a BNC T with a 50 Ohm termination will do.

Very common DIY are two 100 Ohms SMD parallel  😉

[ouraniamge@gmail.com]

Thank you AK2DM and Henrik! Things seem to be working now 🙂

Best,

Ourania Glezakou-Elbert

[Henrik_Volkers]

Unless you want so measure slow light intensity, you should increase the sample rate.

PMT are fast... See spec of the tube. 😉

If pulse energy is needed (radiation spectra) pulse forming networks are usually involved with slow sample rates.