\chapter{Module Testing}

Now that the baseplate and components have been lowered into the module vessel, it is now useful to test the integrity of the detector signals. This must be done prior to the module being installed into the scattering chamber.

First the pre-amplifier packs must be attached to the back of the baseplate. See Figure 5.1.

\begin{figure}[ht]
\vspace{12cm}
\special{psfile = /home/oed/Modprotocol2/backbase.ps
hscale=90 vscale=90 hoffset=-30 voffset =-210}
\caption{Module baseplate (back view).}
\end{figure}

The pre-amplifier cans each require four long threaded rods to fix them in place. The rods are of two sizes, 174mm and 187 mm. The shorter rods are used for the central pre-amplifier can, and the longer rods are used for the outer pre-amplifier cans. These screw into the holes provided on the back of the baseplate. The pre-amplifier can is lowered over the four threaded rods such that they run along the inside of the pre-amplifier can cover, and protrude through the holes in the lid of the pre-amplifier. The orientation of the pre-amplifier packs is shown in ``The MEGHA manual'', page 18, figure 2.7. 
The pre-amplifier pack has three black female connectors at the bottom. These should be lowered carefully onto the glass feedthrough pins at the back of the baseplate. Once this is done the lid of the can may be secured down using nuts and washers. The rods for the outer pre-amplifier cans are longer than those for the inner one so as to accommodate handles. The handles are made out of cast iron and have four holes tapped into them. The handles sit over the two outer threaded rods, and are fastened down with nuts and washers.
Now that the module has been assembled, we can test it to see if all the signals from the detectors are present.

\section{Pulser Testing of the Pre-amplifier Pack}

N.B. \em Bias must not be applied to the detectors while pumping the module. Bias applied to the detectors while pumping (or venting) could result in spark discharge, severely damaging them.
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\rm Place the module on a sterile surface such that the top of the pre-amplifier cans are facing upwards. The power rails of the pre-amplifier packs each require $\pm$12 volts. First connect up the power to the pre-amplifier.
 At this stage the module does not need evacuating and bias should not be applied to the detectors. Each pre-amplifier pack is associated with three telescopes. Which are labeled on the back of the packs, A, B and C.
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N.B. \em ``The MEGHA manual'', defines the different connections on the back of the pre-amplifier pack. See page 18, figure 2.7 of that manual.
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\rm Each pre-amplifier pack has three inputs devoted to test signals, these are, E$_{T}$, P$_{T}$ and G$_{T}$. These inputs  allow a pulser to be driven into the pre-amplifier pack, and to be looked at after pre-amplification. Any distortion of the pulser signal after pre-amplification draws our attention to a possible problem with the pre-amplifier pack in question.
The pulser enters the pre-amplifier via these test inputs and travels around the internal pre-amplifiers and PCB's as a normal signal from an experiment would. The pulser is output to one of the corresponding signal output points, i.e. G, E, a, b, c, d. For example, by placing a pulser into E$_{T}$, of one pre-amplifier pack, we expect the same pulser to be seen at the output E for all three telescopes, A,B and C. In this way we test that the E channel of the pre-amplifier is amplifying correctly.
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N.B. \em The central pre-amplifier pack for the centre module, only represents two telescopes, as the central telescope does not exist due to the beam-line.\\
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\rm The same tests can be performed for, P$_{T}$, G$_{T}$. Figure 5.2 shows the experimental setup required.
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N.B. \em  a,b,c,d correspond to P$_{T}$. E corresponds to E$_{T}$. G corresponds to G$_{T}$.
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\begin{figure}[ht]
\vspace{5cm}
\special{psfile = /home/oed/Modprotocol2/Electronic.ps
hscale=90 vscale=90 hoffset=-90 voffset =-285}
\caption{Experimental setup for pre-amplifier pack pulser testing.}
\end{figure}

\rm Hence using a pulse generator, put a pulse successively into E$_{T}$, P$_{T}$ and G$_{T}$, for each pre-amplifier pack. Make sure that the pulser can be seen in every corresponding output channel respectively. The reproduced pulser signal should be very clean with little noise.
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N.B. \em If a signal is missing, it may be necessary to replace the entire pre-amplifier pack if the reason cannot be diagnosed. Also due to the high gain of the gas signal pre-amplifier, feedthrough of the gas signal onto the position and energy outputs is common. This however is not a problem and should be ignored.
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\rm The energy signal and position signal use the same gain pre-amplifier, and hence the pulser output for both will be the same. The gas signal however uses a gain five pre-amplifier and hence the pulser amplitude will be greater.
After testing all the pulser channels, for all three pre-amplifier packs, remove the power from the pre-amplifier packs, as well as the pulsers.

\section{CsI Scintillator Testing, using a Pulser}

It is possible to apply a pulser to all the scintillators, to make sure that the pre-amplifier of each is working correctly. The CsI scintillators have a separate power rail and bias line to the other detectors (see Figure 5.3) and are hence totally separate to the pre-amplifier packs. 
The pulser is applied to the scintillators via pin 13 (see Figure 5.3). This supplies all the scintillators with a pulser signal, via the ribbon cable discussed earlier. A female connector (attached to twelve cables) seats on the CsI feedthrough. The $\pm$12 volts power is applied through these cables to pins 4 and 5 on the feedthrough (see Figure 5.3). The bias at this point is not required.
After application of the power and pulser, the pre-amplified pulser signal from each scintillator can be reproduced using the setup in Figure 5.4. Each scintillator should have a reproduced pulser signal. Any that do not may have a faulty pre-amplifier and hence need replacing.
After testing remove the pulser and power from the scintillators.

\begin{figure}[ht]
\vspace{11cm}
\special{psfile = /home/oed/Modprotocol2/CsI2.ps
hscale=90 vscale=90 hoffset=-56 voffset =-210}
\caption{CsI scintillator pin allocation.}
\end{figure}

\begin{figure}[ht]
\vspace{5cm}
\special{psfile = /home/oed/Modprotocol2/Electronic2.ps
hscale=90 vscale=90 hoffset=-90 voffset =-320}
\caption{Experimental setup for CsI scintillator pulser testing.}
\end{figure}


\section{$\alpha$-Source Testing}
Using an $\alpha$-source it is possible to test the signal integrity of the PSD's and CsI scintillators. 
To do this place the source underneath the telescope that is to be tested. This is done by removing the module vessel from the baseplate, and placing the source on the inside of the vessel, against the blanking plate. Carefully lower the detectors into the vessel, (making sure that the $\alpha$-source is not disturbed, and that the O-ring around the perimeter of the baseplate stays in place), such that the pre-amplifier pack are facing upwards. 
At this stage you should now have an $\alpha$-source directly beneath one of the telescopes.
The source used is preferably mixed, so that a quick test of the energy resolution of the PSD can be made. The E signal from the PSD should be able to resolve all the $\alpha$ peaks in the source.   

At this stage power, $\pm$12 volts, should be supplied to both the pre-amplifier packs and to the CsI scintillators. Pulsers to the pre-amplifier packs and scintillators should be removed.
Due to using an $\alpha$-source, the module will need evacuating. Assuming that a pump is available, attach the pump to the large SwageloK fitting on the back of the baseplate, (ensuring that the small Swagelok fitting has a cap nut screwed onto it), and begin to pump the module down. Due to pumping, the module vessel and baseplate should form an air tight seal, without the need of bolting the two together.
Once the vessel is at a suitable pressure, the bias may be applied to the scintillators (typically 30V) and to the PSD's (typically 60V). The bias is applied to the scintillators via pin 1 of the scintillator glass feedthrough (see Figure 5.3).
On the back of each pre-amplifier pack there are three SHV connectors labeled A,B and C. These correspond to the three telescopes also labeled A,B and C. Apply bias to the PSD under which the $\alpha$-source was placed via the appropriate SHV connector. Using the setup shown in Figure 5.5, a bipolar signal produced by the $\alpha$ particles incident on the scintillators and PSD's may be viewed. Only one signal is produced by each scintillator, and these are carried out via pins 2,3,6,7,8,9,10,11 and 14 of the scintillator feedthrough. Each PSD however produces five signals, a,b,c,d and e. So each PSD should be tested to make sure that all five signals are there. It will be noticed that the PSD energy signal is stronger than the four corner signals. Each scintillator and PSD must have all their signals present. If a signal is missing then either the pre-amplifier is faulty or the detector. Pre-amplifier faults will be evident during pulser testing however.

\begin{figure}[ht]
\vspace{12cm}
\special{psfile = /home/oed/Modprotocol2/Electronic3.ps
hscale=90 vscale=90 hoffset=-60 voffset =-220}
\caption{Experimental setup for $\alpha$-source testing.}
\end{figure}

Each of the telescopes should be tested in this way. After testing one telescope remove the bias and bring the module back up to air. Then move the $\alpha$-source to a new telescope and repeat the procedure out-lined above.
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N.B. \em Remember to remove bias before evacuating or bringing the module up to air.
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