**Date:** 21 March 2001

**Project:** Intercryostat Detector Electronics

**Subject:** Low Voltage Distribution

This note and supplemental documents describe the low voltage
distribution system designed to deliver power to the Intercryostat
Detector (ICD) preamplifiers (preamps).

**General Information**

The preamps used by the ICD are the I-type version of those used in the
rest of the calorimeter readout, differing only in the integrating
capacitor value (22pF) and two resistors in the output shaping circuit,
which "stretches" the ICD PMT signal to look like a calorimeter signal.
These preamps are mounted on circuit boards (six per board), and each
board is housed in an ICD electronics "drawer". These drawers also
contain the photomultiplier tubes (PMTs) and the high voltage bases for
the PMTs. The drawers are installed into ICD crates (16 per crate) which
are mounted beneath the cable winders in each detector quadrant. The ICD
signal readout is part of the calorimeter BLS/ADC system.

The following electronics systems used by the ICD are identical with the
calorimeter as a whole, and are described in their corresponding
Operational Readiness Review documents:

-   The preamps.

-   The preamp power supply.

-   The high voltage power supply. (In addition, a document detailing
    the safe usage of the ICD high voltage distribution system was
    submitted and accepted.)

-   The preamp pulser and fan-out card.

-   The pulser power supply.

-   The BLS/ADC readout.

Those items unique to the ICD electronics are the low voltage fan-out
system, electronics drawers, voltage supply cables, and the racks in
which the power supplies are mounted. Figure 1 shows the general layout
of the ICD tiles and crates.

The low voltage for the ICD preamps is supplied by a custom
VME-controlled power supply, designed by Dave Huffman of FNAL. It is
identical in operation to a calorimeter low voltage power supply. The
ICD low voltage power supply is located on rack PW09 on the western side
of the platform (Figures 2-4). The power supply will provide three
separate voltages: 8 V @ 10 Amps, 12 V @ 10 Amps and --6 V @ 10 Amps.
The power will be supplied to each of the 48 ICD electronics drawers.
The voltage and current can be monitored via a computer connection. If
any voltage or current exceeds a set level, all output voltages will be
disabled. This is done to prevent the application of partial power to
the preamps. The supplies are fused on the primary 208 V AC input and
the DC output. A solid state 3-phase relay is used to control the
application of AC power to the supply. There is a local On/Off, Reset
and Local/Remote switch on the front panel. There are LED indicators on
the front panel showing the status of the supply.

**Requirements**

The design must meet all Fermilab electrical safety standards and all
components must be rated for the maximum current and temperatures to
which they will be exposed. Voltages delivered to the preamplifiers must
be within 0.1V of the nominal values.

**Details of Implementation**

The power path from the wall socket to the fan-out card is shown in
Figures 5-9. One power supply provides the three voltages to each of the
four ICD crates. Each voltage and associated ground is split 1:4 by
Stinger gold plated power distribution blocks (SDB2 4 GA to 10 GA). The
splitters are mounted with nylon screws to a panel installed near the
bottom of the PW09 rack (Figures 12-13). Three pairs of conductors are
required to distribute each of the three voltages and associated grounds
to the four quadrants. For each quadrant, one three-conductor
(202-10-3503) and one four-conductor (202-10-3504) Okonite-FMR 10 AWG
cable are used. The insulated conductors are UL rated VW-1, and pass
vertical tray flame test of UL 1277 for type TC power and control tray
cable. The 90ºC wet or dry ampacity of the Okonite cables is 30 Amps per
conductor. The calorimeter low voltage power supply provides a maximum
10 Amps at each voltage. The large size cable was picked primarily to
minimize the voltage drop between the supply and the preamplifiers. One
of the conductors in the three-conductor cable is not used.

The Okonite cables are routed to the ICD crates at each detector
quadrant via the false platform floor, the vertical chutes and the cable
winders. The low voltages are distributed to the ICD drawers through a
fan-out card mounted below the ICD crates. The fan-out card is a long PC
board with individual fuses for each voltage to each drawer. Three pairs
of conductors are fed into a terminal block (Divisible Europa Strip).
The block is a 6-pole strip rated at 40 Amps with a maximum thickness of
a 10 AWG conductor. The terminal block is connected to the fan-out card
via short runs of hookup wire, soldered directly to the PC board. The
voltages for each drawer are fused with GMA 5 x 20 mm fast-acting glass
fuses, rated to 500 mAmps. The voltages are fed to the ICD drawers by
short patch cables, which are Alpha brand, item 6428, multi-pair
foil-shielded tray cable, 18 AWG, UL type CM/PLTC, CSA PCC ft4. The
patch cable with the foil shield and outer plastic jacket removed was
also used to fashion the cable harness within the low voltage fan-out.
Similar 22 AWG wire is used for the jumpers from the fan-out PC board to
the bulkhead connectors. Figure 10 shows a photo of an assembled low
voltage fan-out with the pulser fan-out and cables attached. Figure 4
shows a schematic of the low voltage fan-out card and fuse layout.

Also housed with the low voltage fan-out card is the fan-out card for
the ICD pulser system. This pulser system is identical to the
calorimeter pulser system, and has been reviewed as part of the
calorimeter preamp pORC review. The pulser and pulser power supply are
mounted in the same rack (PW09) as the ICD low voltage power supply.

The low voltage fan-out is mounted in a custom-made aluminum box
isolated by plastic washers. The pulser fan-out is mounted to the back
of the low voltage fan-out by plastic standoff posts. The low voltage
supply cables enter the low voltage fan-out housing via a rectangular
aperture in the side. The supply cables attach to a Divisible Europa
Strip connection block mounted on the back of the housing. A cable
harness consisting of 18 AWG hookup wire is connected to the Europa
strip at one end, and soldered to the low voltage fan-out PC board at
the other end. A similar hookup wire is used to connect each voltage,
via a fuse, to a bulkhead connector mounted on the front of the low
voltage fan-out housing. The multi-pair patch cables connect to the
bulkheads and the corresponding connectors on the ICD drawers. The
pulser current supply cables and the pulser com-mand cables which run
from the PW09 rack enter through the other side aperture. The pulser
fan-out cables exit through a long narrow slit on the front of the
housing and are

connected to the ICD drawers. The low voltage housing is mounted below
the ICD crate, with a large mounting screw at each side. Figure 11 shows
a mounted fan-out in place below one of the ICD crates.

**Rack Monitor Interface**

Each LED is green if conditions are normal and red if a fault has been
triggered. A fault will remain once triggered, and the associated LED
will remain red until a computer gen-erated reset occurs or until the
RESET button is pressed. The control of the rack monitor interface is
via a cable from the 1553 to a 37-pin D connector. The only control
function available is RESET.

The smoke detector sensor is connected into a wire harness that enters
the rear of the

rack monitor interface. A +20 V and ground are supplied to the smoke
detector. The

+20 V is interrupted when a RESET occurs to clear the detector
condition. The RESET

is supplied by a front panel push button or by an output bit from the
1553. A fault occurs

if the detector smells smoke or if the cable is disconnected. If a fault
occurs, the front

panel Smoke Detector LED is lit, the annunciator is activated and the
OK/Smoke bit supplied to the 1553 changes to indicate smoke. A Fault Out
signal is produced to disable the power supply.

Figure 1: Conceptual view of the ICD layout

![](media/image2.png){width="6.0in" height="7.75in"}

# Fig. 2: Conceptual Layout of the ICD Low Voltage Distribution System

![](media/image3.png){width="6.0in" height="4.5in"}

Figure 11: ICD low voltage fan-out mounted below an ICD crate.

![](media/image4.jpeg){width="5.013194444444444in"
height="3.7597222222222224in"}

Figure 12: Input cables from low voltage power supply to splitter.

![](media/image5.png)

Figure 13: Low voltage splitter panel.

![](media/image6.jpeg){width="4.972916666666666in"
height="3.729861111111111in"}

Figure 14: Terminal block for low voltage fan-out.

![](media/image7.jpeg){width="4.886111111111111in"
height="3.6444444444444444in"}

Figure 15: Segment of low voltage fan-out board.

![](media/image8.jpeg){width="5.319444444444445in"
height="3.9694444444444446in"}

Figure 16: Fan-out connectors for output of low voltage to ICD drawers.