Fujifilm FCR XG-1 X-ray Scanner, Photomultiplier Tube Reverse-engineering (Part 3 of 3)

Reverse engineering of the Fujifilm PMT12A PMT module that contains the photomultiplier tube, high voltage power supply and analog amplifier from a Fujifilm FCR XG-1 …

Fujifilm Photomultiplier Tube

Introduction

The teardown of a Fujifilm FCR XG-1 X-ray image scanner for computed radiography became the basis for this reverse engineering project. You can see the teardown of the entire Fujifilm FCR XG-1 machine here and the teardown of the polygon laser scanner module here.

A short introduction, computed radiography is based on reusable phosphor imaging plates, the plate is used instead of film. The x-ray exposed imaging plate is scanned with a red laser timed to a photomultiplier tube to read out the single pixels on the imaging plate. The returned light from the scanning laser has a different intensity dependent on the amount of absorbed x-ray energy and thus the photomultiplier tube can translate this into a 12-bit grey scale resolution.

This article covers the reverse engineering of the Fujifilm PMT12A PMT module that contains the photomultiplier tube, high voltage power supply and analog amplifier.

 

Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

Read this document about safety! http://www.pupman.com/safety.htm

 

Reverse engineering

The photomultiplier assembly is mounted on a sheet metal holder with the tube going out through a grounded layer of mu-metal for shielding the tube from electrostatic interference. The PCB has a output amplifier and power supply part on the left side of the socket and a high voltage power supply module on the right side.

The Fujifilm PMT12A board has two connectors, which both went to the SCN12A card in the main computer of the Fujifilm FCR XG-1 scanner. CN1 is a 34-pin flatband pin header and CN2 is a coaxial output signal from the output amplifier.

The output amplifier is shielded, the differential amplifiers on the board is using +12/-12VDC from a LM2940CT and LM2990T regulators, as the +15/-15VDC input goes directly to the HV module. The Hamamatsu C7775 from 2007 does not have any datasheets available online, but browsing through the newest modules shows that they still make a C-series 5 pin HV module, that turns out to use the same pin layout as its earlier modules.

From the pin 5 of the C7775 comes the negative high voltage supply for the photomultiplier tube. The cathode of the tube is connected to the 4 blue capacitors that is tied to ground, to ensure a stable voltage at the start of the high voltage chain.

As more electrons are accelerated from the first dynode to the next and so on, less current is needed to drive them on, this is done with a pure resistive divider network between the dynodes, but it has its drawbacks with loss of linearity and output deviation in the region of 10-20% at high output current. A improved divider network uses capacitors to insure stable supply voltage at peaks and even individual power supplies for each dynode can be used to do the same.

From the photomultiplier tube handbooks from Hamamatsu, the requirements to a PMT high voltage power supply reveals that quality control is needed to achieve a line/load regulation at +/- 0.2% and ripple noise/temperature drift at 0.05%. The Hamamatsu R1848-07 photomultiplier tube is a 10-stage 14-pin version that can use up to -2500V dynode supply.

It took a great deal of cutting with a new sharp box cutter, to get in-between the acrylic light guide and the blue glass filter window of the photomultiplier tube. It took about an hour to free the two parts from each-other, without harming tube or light guide.

Schematics

Schematic from the service manual. I marked the needed pins for the module to run without the computer/scanner analog-to-digital conversion modules.

PCB test points and connections schematic

Experimentation: Getting the unit to run and scintillation plastic for radiation detection

6th June 2021

After having seen the connection diagrams in the manual, I was confident to test the module with power on. I was using a power supply with +15 VDC, -15 VDC and GND. I shielded the window of the PMT with aluminium foil to block out any light. A powered up photomultiplier tube that is flooded with light risk burning holes in its dynodes! Protect and treat your PMT with great care.

Judging from the computer power supply of +5 VDC and the datasheet for the Hamamatsu C9619 high voltage power supply, I tried my luck with putting +5 VDC on the input pins I had located. It was also mentioned in the manual that the module has a “high voltage hardware ok” and “high voltage software ok ” signal, that both had to be high for the high voltage to get active. It turns out that the input pin 5, labelled HVSH is “High Voltage Software High”. When +5 VDC is applied to pin 5 the high voltage supply is generating -510 VDC.

The output signal is sine wave like waveform with 1, 2 or 3 peaks, depending on the signal strength. The highest peak was up to 70V, but I am not sure that the scaling was correct from these measurements. I unfortunately lost all my oscilloscope screenshots to a defective USB stick 🙁

A photomultiplier tube can be a very sensitive instrument, depending on the negative supply voltage for the dynodes. From the PMT handbooks graphs show that common PMT behavior the amplification is highly dependent on the high voltage supply. The -510 VDC this module uses gives a mere amplification of 40.000 times. This level of amplification is sufficient for the computed radiography, but for a more interesting task like radiation detection with a scintillation crystal, it is suggested that -1 to -2 kV is needed for a amplification of 20.000.000 times and up towards 1.000.000.000 times.

 Demonstration

Teardown, reverse engineering and test of the Fujifilm PMT12A board.

References

[1] Hamamatsu, “Photomultiplier Tubes – Construction and Operating Characteristics”, January 1998.

[2] Hamamatsu, “Photomultiplier Tubes – Basics and Applications”, Third edition, Handbook, 2006.

Fujifilm FCR XG-1 X-ray Laser Module Teardown (Part 2 of 3)

Part 2: Teardown of the laser scanner module from a Fujifilm FCR XG-1 x-ray image scanner / digitizer. Also known as Computerized Radiography (CR), it …

Fujifilm FCR XG-1 X-ray Image Scanner Teardown (Part 1 of 3)

Part 1: Teardown of a Fujifilm FCR XG-1 x-ray image scanner / digitizer. Also known as Computerized Radiography (CR), it fulfills the job of scanning …

AGFA ADC 5155 Photo Multiplier Tube (Part 4 of 4)

Teardown of the photomultiplier tube assembly (PMT) and its high voltage power supply. The high voltage power supply and PMT is reverse-engineering to use the …

AGFA ADC 5155 Laser Module Teardown (Part 3 of 4)

Teardown of a AGFA ADC 5155 x-ray image scanner / digitizer. Also known as Computerized Radiography (CR) it fulfills the job of scanning a x-ray …

Agfa ADC 5155 Motorola 68K Computer Teardown (Part 2 of 4)

This is the reverse engineering and teardown of a very interesting computer that runs on VME framework developed for the Motorola 68000 series CPUs. It runs a custom operating system called Monitor 4.28 developed by Agfa-Gevaert NV, Belgium.

AGFA ADC 5155 X-ray Scanner Teardown (Part 1 of 4)

Part 1: Teardown of a AGFA ADC 5155 x-ray image scanner / digitizer. Also known as Computerized Radiography (CR) it fulfills the job of scanning …

Future Projects, Teardowns and Power Electronics – Isolation, Day 22

A look into what the future brings of projects, teardowns and power electronics. Simple, complex, small and large, there will be it all, stay tuned!

70 kV / 65 kW X-Ray System, Transformer and Inverter – Isolation, Day 12

I give an overview of a 65kW X-ray generator system for a 70 kV X-ray transformer. The fullbridge of 400A 1200V IGBT bricks makes for …

High Voltage Transformers – Isolation, Day 9

I go through my collection of iron/ferrite core high voltage transformers. MOTs, OBITs, NSTs, PTs and X-ray transformers. Microwave Oven-, Oil burner ignition-, neon sign- …

Siemens Polyphos 30, X-RAY Inverter and Control Panel Teardown (Part 3 of 3)

Teardown of the Siemens Polyphos 30 X-ray systems control panel including computer, safety functions, HMI and high voltage inverter circuit.

Siemens Polyphos 30, X-RAY Collimator and Image Plate Teardown (Part 2 of 3)

Teardown of the Siemens Polyphos 30 collimator and image plate. Collimator had an interesting moving blinds design with a lot of gears, pulleys and strings. …

Siemens Polyphos 30, X-RAY 125kV head teardown (part 1 of 3)

Teardown of the Siemens Polyphos 30 X-ray head which contains step-up transformers, voltage multipliers and a rotating plate x-ray tube and a lot of oil! …

Merry Christmas & Happy New Year 2018 (X-ray teardown edition)

Pictures as promised: https://highvoltageforum.net/index.php?topic=523.0 Teaser for the upcoming teardown videos of the Siemens Polyphos 30 x-ray machine, complete with control panel, inverter, collimator, detector/grid plate …

GE AMX-II, mobile 110kV X-RAY system teardown

Teardown of SCR inverter controller, driver and bridge for a General Electric mobile x-ray unit, the AMX-II. Features a 120V battery operated apparatus from 1979 …