LI Pulser Box and Fibre Bundle Tests

Intro:

Need to test pulser boxes and light injection fibres bundles upon arrival at Soudan
Pulser boxes are installed, one in each electronics crate on the middle level, in the space above the Wener power supply and below the RPS unit
Light injection fibre bundles are installed to the planes before each plane is lifted, (see installation Word document written by Richard White, Sussex for more details)

Testing of pulser boxes involves:

checking that electronics boards inside pulser boxes have not been dislodged in transit
checking that all LEDs are working
checking for broken fibres
measuring light emitted from each fibre in each connector at the pulser box via 1m test fibre bundle

Testing of fibre bundles involves:

checking for damaged fibre bundles and broken fibres before installation
measuring % transmission of fibres compared to a 1 metre test fibre (from pulser box tests)

All measurements are made using Sussex testing apparatus.
Measurements are currently written into a root tree; for instructions, follow this link.

This is a pulser box. The three lights at the top on the front are, from left to right: power (red), ready (yellow) and pulsing (blue). Beneath, from left to right, there is: the RS232 connector which is connected via the green cable to the EDAS connection on the RPS unit; the red reset button; the external trigger BNC connector; something I can't remember; the pulse monitor; fuse; and on/off power switch.

Outline:

Sussex Test Apparatus

Consists of a set of 20 PIN diodes, calibrated to have identical responses, connected to a single amplifier.
A fibre bundle is connected at one end to the pulser box via a 20-way connector and at the other to the box containing the PIN diodes. The fibres have metal connectors at the end and can be plugged directly into recesses in the PIN diode box, one fibre per PIN.
Only a single fibre is pulsed at a time by the pulser box, (a result of the fact that only a single LED can be pulsed at a time in the pulser box), and so only light from one fibre at a time is amplified.
The signal from the amplifier is sent to a picoscope which has a PC interface. The picoscope is triggered by a signal from a BNC connection on the front of the pulser box. This sends out a constant 4V signal when the box is on. When the pulser pulses the signal dips to below 0V for a short time.
The PC controls both the flashing of the pulser box and the analysis of the pulses as sampled by the picoscope. A set of three LabView programs can be used for controlling the pulser box and for sampling the pulse heights of the signals measured by the PINs, (see separate document for use of the LabView programs).

This is the picoscope. Channel A is connected with the T-junction. The signal from the PIN array amplifier is split to go to the pico and to an oscilloscope. Channel B is connected to the pulse monitor on the front of the pulser box. At the rear of the box a parrallel port connector is seen. This is connected to the parrallel port of the LI laptop.

Testing a Pulser Box

A pulser box contains 20 LEDs and is controlled via an RS232 cable from the serial port of a Laptop or over ethernet via an EDAS box. The boxes have 64 regular connectors, each with 20 fibres, one from each of the LEDs in the box. There is also one spare connector and two connectors for PIN fibres that go to PIN diodes on the front end electronics boards mounted on each MUX box. The fibres in the PIN connectors are made to be significantly brighter than the other fibres, as PIN diodes are not as sensitive as PMTs to low light levels.
LABELLING THE CONNECTORS ON THE BACK OF THE PULSER BOX: connectors are labelled in order of plane number they serve (i.e. the connector serving east side of plane 65 will be connector 1 on pulser box 2, west side of plane 100 will be connector 36 on pulser box 3); Connector 65 on a box is the SPARE, 66 is the LOW gain PIN and 67 is the HIGH gain PIN connector. (Also see LI mapping page.)

Using an Allen key the front of the pulser box can be opened. Open carefully as there are wires from electronics boards within the box soldered to the front panel. Check that the electronics boards have remained firmly in place after shipping. If not, reseat the boards.
Remove the blacking connectors at the back of the pulser box and use the LabView sequential flasher vi program, to check that there are no broken fibres in the box and that all the LEDs are working. If there are broken fibres, contact Phil Harris for advice.
If the same fibre position in all connectors always looks dark, this implies an LED problem. Burnt out LEDs can be replaced inside the pulser box. Again if this has to be done, contact Phil Harris for advice.
To test the light output from each fibre from each connector, connect the 1 metre test cable to one of the positions on the back of the pulser box (see section below "Attaching Fibre Bundles to Pulser Boxes") and connect the single fibre ends to the appropriate position in the 20-PIN diode array, (always connecting fibre 1 to PIN 1, etc. removes any possible error due to variations in the PIN diode responses. This is important later when measuring the transmission of the fibre bundles compared to the test fibres).
Run the appropriate LabView program using the settings stated in the LabView document and save the text file produced. The file lists the average value for the peak of the pulse in millivolts as measured by the picoscope, for each LED, i.e. for each fibre in that connector.
Once all connectors have been measured, use root macro to write all the information into a tree, (see instructions on how to do this here).

This is the back of the pulser box. Each of these connectors need to be tested for light output using the test setup. Each connector has 20 fibres, one fibre from each LED in the box. The 64 connectors which supply light to the scintillator modules are the 4 groups of 16 that can be seen. The bottom three connectors are, from left to right: spare, low PIN and high PIN connectors. To the right of the high PIN connector is the connection for the single trigger fibre; and to the right of that is the power lead which is just plugged into the wall supply.

Testing Fibre Bundles

Each fibre bundle consists of 20 clear fibres of varying lengths with a 20-way connector at one end and individual metal connectors at the other. The 20-way is plugged into the back of the pulser box to the spare connector (see section below "Attaching Fibre Bundles to Pulser Boxes") and the 20 fibre ends into the PIN diode box ,(fibre 1 to PIN 1, etc).
Dab the tips of the fibre ends with isopropyl alcohol before inserting them into the PIN diode box. Only use special lens cleaning papers for cleaning.
Unlike in the case of the test cable, the connectors on the individual fibre ends are not designed to fit perfectly into the PIN diode box, so ensure that the fibres are pushed in as far a they can go.
Once again the LabView program can then be run using appropriate settings and a text file saved for each fibre bundle.
The data for each bundle can be added to an existing tree containing all the values for the % transmission for all the LI fibres, (see instructions on how to do this here).
ENSURE THAT PULSER BOX DOES NOT CONTINUE TO PULSE AFTER TESTING. THIS CAN CAUSE PREMATURE LED DEATH! If blue LED on front of pulser box is on when you expect pulser box to be off, hit the red reset button on the front panel.

This is the test setup. The grey box is the array of 20 PIN diodes. A fibre bundle is currently plugged into the box. The other end of the fibre bundle is plugged into the back of the pulser box itself. Notice that care was taken when plugging in the fibre bundle to stay clear of the minimum bend radius of the fibre which is approximately 1 inch. Also notice in this photo, the serial and parrallel port connections in the back of the laptop coming from the pulser box and the picoscope respectively.

Attaching Fibre Bundles to Pulser Boxes

Use isopropyl alcohol to clean the 20-way connector and it's mate before connecting the bundle at the pulser box end. Only use special lens cleaning papers for cleaning.
Make sure that step dowels are used when testing fibre bundles; this causes the connectors to be installed upside-down. (IMPORTANT: Check whether or not the connector needs step-dowels. In some cases e.g. the 1m test cable and the first 4 sets of PIN fibres, the connectors were made correctly and step-dowels are not necessary. If step dowels are needed, an offset between the fibres in a pulser box connector and the fibres in the fibre bundle connector can clearly be seen.)
If grease is to be used, use a syringe to put a small amout of grease along the length of the connector, over the fibres. Then use a latex glove and in one motion smear the grease along the connector. Push the connectors together and tighten screws without allowing the connectors to come apart. (If the connectors do come apart, air bubbles may be introduced which will ruin the optical connection.)
Use washers on the screws when attaching the fibre bundles to the pulser box. Be sure not to overtighten the screws.
Use a strip of black insulating tape to light tight the pulser box-fibre bundle connection.

This is an example of a 20-way connector from a fibre bundle connected to the back of a pulser box. Notice that the connector is upside-down due to the insertion of the step dowels. Also the strip of black tape ensures that the connection is light tight.

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