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Howto Adjust the EMC PIN Diodes

This file is $BFROOT/www/Detector/Calorimeter/Operations/pages/HOWTO-PinDiode.html.
Feel free to add/update/remove items on this page.

There are four sensors around the beam pipe near the calorimeter endcap (EMC), which provide a measure of the radiation exposure of the EMC endcap. Each sensor consists of a small CsI(Tl) crystal read out by a PIN diode (like a mini-calorimeter). The signals of four diodes are added together, so there is one EMC signal.

The EMC diodes inhibit injection when their signal reaches 0.7 V.

This voltage can be read from EPICs at the bottom of the Bkg page linked of the Main one.

If the EMC diode is regularly inhibiting injection and the reading is more than 0.1 V with no beam then it probably needs adjusting.

To do that:
Go to the "Bldg.624 power supply alcove": the room up the stairs in the IR2 hall on the far side from where the door to the control room is (past the chillers).

Look for rack B624-06 (about the third row in, 4or 5th rack in) Underneath the keyboard is a board marked EMC on top and PIN DIODE underneath. Just in the rack to the left of where this guy is pointing.

Immediately below the 'EMC' label on the board there are a collection of 8 screws (each with two associated lemo ports).
There are two screws which are of use here:

The first is the uppermost screw next to the purple lemo connector (in the socket marked total). This screw allows you to adjust the PIN diode THRESHOLD. This should not be done unless circumstances really call for it!

The second (and most relevant) screw is the 8th one in the set (i.e. the lowest). It is marked 'OFF SET' and has a lemo connector plugged into one of the ports immediately left of it. This is the screw for the VOLTAGE. To lower the value turn the screw anti-clockwise (and vice-versa). Keep an eye on the EPICS voltage reading and adjust it until it is close to 0V when there are no beams. If you do not have a laptop with wireless you can use a voltmeter plugged into the connectors marked total.

Some of this is poached of the Liaison Shifter Instructions which also tells you how to bypass the injection inhibit if necessary. Also more information on these diodes can be found here .

Page author: Wahid Bhimji
Last modified: Jan 17, 2003