New Keysight Agilent U3401A Bench Multimeter

I recently purchased a new multimeter for use in the lab. I have two handheld digital multimeters but having a bench meter would work for me quite well to save me from reaching for the handheld and finding space for it when i'm working on something.

The Keysight U3401A is a budget / entry level 4 1/2 digit DMM from Keysight, although lacking in some features it will be fine for my needs and even this entry level offers me some technical advantages over my handheld meters. Most notably; higher voltage (upto 1.2kV) and current ranges (upto 20A), greater accuracy and resolution across the board. Voltage is 0.02%+4, current 0.05%+4 or 5 depending on range, resistance 0.1%+3 or 6 depending on range.

The Keysight U3401A was purchased through a member of the EEVblog forum for exactly £200.00 including shipping, as a customer return from Element14. The unit is within calibration and under manufacturers warranty, even the test leads had not been opened. Of course this was a one-off deal.

The new Keysight U3401A DMM sat on top of my two Hewlett Packard 6632B DC Power Supplies (aka Agilent then Keysight!) next to my faithful Xytronic LF-1000 soldering station.

My current two meters are:

Sinometer / Mastech MAS-343 with tape to prevent changes because this is exclusively connected and used with my Testec HVP-40 high voltage probe.

Fluke 107, a budget meter aimed at the Asian markets. It's a great value meter and one i would highly recommend to beginners who need something reasonably priced but built well and one that meets it's safety specifications.

Next Teardown: Perkin Elmer LS5 Luminescence Spectrometer

Fresh from ebay, wheeling the latest lump into the shed! Might be a week or so before you see this one attacked with a screwdriver.

Liquid Scintillation Analyser Parts Haul

While i still need to take a more detailed look at the sample loading and electronics for the Packard 1000 TR Liquid Scintillation Analyser i thought i would do a quick update listing out the total haul from this.

So the analyser itself was bought off ebay from a seller local to me so there was no shipping, which would have been a problem otherwise due to it's weight any shipping costs would have been a problem.

I salvaged:

• 1* 5000v AC power supply.
• 2* Hammamatsu R331 Photomultiplier tubes.
• 1* Dual channel adjustable photomultiplier power supply.
• 1* Radioactive source for my collection.
• 1* 2*40 LCD Module
• 64Kg Lead for recycling @ today's price it's just under £1.00 per Kg. I saved about 20Kg for  myself so i can store my radioactive samples.
• Approx 10kg of other recyclable metals; steel, aluminium & brass.

Hopefully over this coming weekend i will be able to finish looking at the electronics and that sample load/unload mechanism. Though i dont expect to find anything more salvageable.

Testing a 5000v Power Supply (Neon Sign Transformer)

I took a quick look at the power supply that was used for the ionizer in the liquid scintillation analyzer. It's a Chapman brand 120v input with 5000v output. I believe this is essentially a neon sign transformer with integral ballast/current limiting.

After removing the electrodes i just wired it into my variac to run it upto it's rated 120v input and positioned the output close to the ground wire for some sparkly action. The output is dead on 5000v AC with an input voltage of 120v.

This should make some interesting videos in the future. Especially if i can find some things to zap and also increase the input voltage beyond the 120v rating.

Modifying a Packard / Perkin Elmer Photomultiplier PSU

Today i took a deeper look at the packard photomultiplier power supply i removed from the LSA i recently took apart. It has a Packard part number of 7101139.

I wanted to test powering on the PSU from my bench power supply and verify the function of the control input. To allow me to easily use this in future projects. When installed in the 1000 TR LSA 5v was seen on the two input pins which seemed to enable the power supply output at around 1600v.

First i verified the power supply was working. Applied +15v to the power input and +5v to the control line and got the +1600v output i had seen when the unit was in the LSA.

After inspecting the circuit i spotted a MAX584 voltage reference  close to the input with only the 10v output of the reference in use i suspected the board would be adjustable so altered the voltage between 0 and 10v and indeed the supply did alter it's voltage from +970v to +2290v.

I wanted to check the circuit to see if it can be made more stand-alone and still be made adjustable, there are missing trimpots and jumpers on the PCB so wondered if these would allow this.

On closer inspection JMP1 & 2 had a soldered link across two of the three pads with JMP3 unpopulated. These connected the inputs on the control cable connector to the rest of the circuit. In the other position they connected in the two missing trimpots R41 and R42 into the same input.

The pads were cleaned of solder, three pin headers installed and using a salvaged 10kohm trimpot the trimmers allowed full voltage adjustment from +970v to +2150v on each channel. Switching of the JMP3 jumper allows both channels to be turned on or off, but not independently. I maybe able to further modify this two allow that feature.

Soon i will sort out a suitable enclosure, probably with an integrated power supply for connection to the mains and two 10 turn pots to allow voltage adjustment.

Packard 1000 TR Liquid Scintillation Analyser - Part 3 Photomultipliers

The next phase in the teardown is the photomultipliers and sample chamber.

The two PMTs are installed into a long bright silvery metallic tube, i'm not sure if this is just steel or some more exotic alloy for magnetic shielding and background radiation shielding working in combination with the external lead.  It's not like Mu-metal at all but it is paramagnetic. Although lead absorbs much of the background radiation i will also emit secondary radiation due to this absorption. So additional materials can be used specifically to absorb these secondary emissions. Maybe i need a x-ray fluorescence spectrometer to discover what this metal is made from!

PMT & Sample Chamber Assembly

The PMTs are easily removed, they simply slide into the metal tube with plush velour to provide light blocking.

Inside the metal tube there are two metalized plastic reflectors to improve effeciency of the overall process. They attach in the centre of the tube, the PMTs push up against them.

The large photomultipliers are Hammamatsu model R331-08, featuring a frosted concave quartz window. They are 12 stage PMTs running at 1600v. Well below their 2500v rating. They appear to be designed for use in Liquid Scintillation Analysis.

The PMTs plug into a socket which is housed in a brass case with a brazed end. At the moment i dont have a neat way to desolder this so i will look at doing this in the future. Inside the case will be the resistor divider network and connections for the third cable which i am uncertain as it's use.

Packard 1000 TR Liquid Scintillation Analyser - Part 2

Continuing the teardown of this Liquid Scintillation Analyzer

Before disassembly i wanted to discover how the photomultiplier power supply operated. On investigation it was clear it operated quite simply. With three connections to the main control electronics it uses a simple +5v signal to enable each of the two outputs. This means i can re-use the power supply and photomultipliers in future projects.

Photomultiplier Power Supply

Then came removal of the motor control board, which is a simple drive control to operate two 115v AC motors that operate the top light cap and the sample load/unload mechanism.

Sample loading head assembly.

The sample loading assembly is a moderately simple affair. A sliding top allows the insertion of two sizes of sample vial. The location of this slider is indicated to the electronics with two optical sensors indicating if it's in either position.

Below this is a heavy metal bracket that holds an ionizer assembly and an arm that covers the top of the sample chamber. This is operated by one of the motors with two optical sensors and serves to exclude light from the sample chamber with some plush velvet material to aid light blocking.

The ionizer assembly is a heavy brass construction with five electrodes spaced evenly around where the sample vial enters the sample chamber. The ionizer i believe is to remove any static charge on the sample vial from handling. The ionizer power supply is a Chapman brand with an output of 5000v.

Ionizer assembly & electrodes.

The photomultipliers were removed and saved for a future teardown.

After the photomultiplier and sample chamber assembly was removed it was time to find the Barium 133 check source located inside the machine. After some fiddling with the sample load/unload mechanism and removal of the sample loading assembly i was able to see the source. A small metalic object about 4mm in diameter attached to the coiled spring that allows the load/unload mechanism to push the source into the sample chamber.

Barium 133 Source

The Barium source was dated 11 January 1996 with a 18.8 micro Curie activity. Barium 133 has a half life of 10.51 years so as of April 2015 it's current activity is now around 5.5 micro Curies. Measuring this using my Ludlum Model 3 and a SBT-11A Geiger Muller tube reads about 13,000CPM.

Barium 133 Source