PMT/PMA Test
In my drawer I have some PMT's. Most of them comes from NOx analyzers from an ancient time. But some are "only" a decade old.
I also have some TEC coolers, and found a PMT that did have a cooler mounted. I tested the cooler with 12V and the peltier draw 1A, so it is only about 12W.
Next I measured up the cooling temperature, and the small TEC could cool the PMT to about 10°C. This is of course an improvement compared to 20-25°C, but a lot improvements could be done.
The dark current and the S/N will be much improved with a lower temperature.
Also a AD-549 was used as a Pre-amp, this is a good Fet Op-amp. But the OPA-128 is even better, so I will replace the Op as well.
Here is the original TEC on the left, and the new one to the right. I have to adjust the cooler housing to the new size.
The Hot side of the TEC must be fitted to a heat sink. It seems like the new bigger TEC cooler will fit. Some milling work needs too be done.
Milling work done. The new TEC is thinner, a spacer of about 1.5mm needs to be mounted on the hot side.
The TEC-1 is available on the net. The specification is:
With a hot side temp of 50°C it would be possible to reach -20°C, since the delta T is 75°C. However my control software is locked to a duty cycle of 10% to 90%. This because the speed of the timer in dot Net runs stable at about 10ms. Of course could I make a PIC based fast controller, but I will try with this setup first. Temperature controllers is slow by nature. And 90% duty cycle will probably drive the TEC with over 50W.
I made a software to be able to control the peltier cooler. And the software also controls the heat sink fan.
I will also connect to the Pre-amp out, to a 24 bit AD. For this I use a USB-2408 from Measurement Computing. This I/O also reads the TEC temperature.
The PMT with Pre-Amp needs ± 15V, 5V and of course High Voltage. The gain will increase with higher Voltage, but so will the noise. I will test with 800V. Max HV for the tube is 1500V.
This PSU will provide the necessarily Voltages.
Some about PMT's
