BaBar EMC detector grounding and shielding

Original Grounding and shielding plan set out by John Dowdell

• PDF 17-Jan-97

Final Barrel Calorimeter grounding and shielding

General description

The grounding system for the barrel calorimeter is a "star" topology. The centre of the star is the cylinder-minicrate-bulkhead assembly.

There are one main path for the ground, from the IOB power supply grounds to the preamp through the IOB, ADB, bulkhead and FOB. There is one main shielding path from the copper cooling block to the pre-amp box via the IOB and ADB cans, bulkhead and FOB. The ground and shield are connected together through a 10 ohm resistor on the bulkhead board. However a second resistor on the IOB can be used to make this connection if it proves beneficial.

The cylinder is connected to the nominal detector ground. Whilst another leg of the "star" goes to the TRB and EMB

Around the entire system is the outer shield which is presently separate from the inner shielding scheme.

All the power supplies are floating being referenced to ground through the route described in the diagram below.

Diagram

Index to diagram

1. The three power lines, +5V, -5V and +10V are floating at their supplies in the electronics house. Their returns are joined together on the IOB.
2. Power (digital) ground is passed from the IOB to the ADBs on many pins of the two ERNI connectors.
3. The IOB can and each ADB can are connected through pins 1 and 2 of the 50 way ERNI connector.
4. The analogue and digital grounds are connected together under pin 44 of each of the ADCs on the ADB.
5. The analogue ground is passed onto the bulkhead board, twice per pre-amp (A and B) down the middle row of the AMP 250 pin connector (24 pins). The bias grounds enter the bulkhead on a four pin connector. The bulkhead passes the ground to the ADB on pins 50a and 50e of the AMP connector. The ADB then ties the bias ground to analogue ground.
6. The ADB can is connected to the bulhead using the AMP connector shield. The AMP shield is conneted to the upper and lower metal layer of the bulkhead board using many plated through holes.
7. The upper and lower metal layers of the bulkhead make contact with the Minicrate when the crate is screwed together around the bulkhead board. (Since the minicrates were anodysed this coating had to be removed along the inner edge where good electrical contact had to be made to the bulkhead board)
8. The analogue ground passes straight through the bulkhead board on the pins of the AMP connector, (refer to E above)
9. The upper and lower metal layers of the bulkhead are connected to 5 pins (1a,1b,1c,1d,1e) at one end of the 250 pin AMP connector. This ground is then fanned out to pins 1 and 22 of the pre amp cable connectors through a 10 Ohm resistor. Which is connected to the cable shield drain wire.
10. The Minicrate makes electrical contact with the barrel along the inner surface of its fixing flange (not anodysed).
11. At the bottom of the forward end of the barrel a cable is bolted to the cylinder and tied to the nominal detector ground.
12. Each TRB can has a connection to the cylinder through a cable attached at on end to the TRB power cable clamp and at the other end to a minicrate fixing bolt. The TRB cans are mounted on the solenoid but make no electrical contact with it, being insulated by a sheet of thermally conducting foam.
13. The TRB power cables are clamped to the TRB can. In a small cable clamp.
14. The three power lines, +5V, -5V and +10V are floating at their supplies in the electronics house. Their returns are joined together on the TRB. The electrical ground
15. The pre-amp cable shield is connected to the pre-amp box with a small hinged cable clamp. The last 2cm of shield has no insulating covering for this purpose.
16. The copper cooling blocks are bolted to the IOB cans. The heat path is through the cylinder so in order to create a grounding loop a thin sheet of electrically insulating material is placed between the copper blocks and the minicrate flange to which the copper blocks are bolted.
17. The EMB derives its ground from the TRB through th 14 way ribbon cable.

Final Endcap Calorimeter grounding and shielding

Diagram

Index to diagram