STAR FGT Electrical Connections and
Grounding Scheme
Gerard Visser
Indiana University
2/9/2016
Introductory Remarks
This document describes the FGT but many aspects will directly carry over to the IST. An IST document is
in preparation.
This needs some improved presentation here, but for now please just refer to the following two figures
which are taken from FGT collaboration meeting and safety review presentations:
With reference to the above figures: The FGT detector consists of 24 quadrants arranged in 6 disks. The
grounds, i.e., reference points for the preamplifier and for the decoupling capacitors of the GEM bias
voltage, are tied within a disk.1 The disk grounds are electrically isolated from each other and from the
support structures including the rails and the WSC.
The 6 disks are served by 24 FEE assemblies, each FEE assembly serving two half-quadrants. There are
also 24 HV divider boards each serving one quadrant.
Each FEE assembly has a power/signal cable (type 1 in the figures above) going to the patch box
mounted at the TPC wheel just outside the WSC. [Or mounted as part of the WSC structure, tbd pending
discussions ~now.] Each HV divider assembly has a coax HV cable going to a patch (cable-cable, most
likely) just outside the WSC.
In the cable type 1 there is a dedicated ground conductor which carries no currents and is inside the
aluminum foil shield with the other conductors. Additionally there is the aluminum foil shield and drain
wire which carry no currents and which optionally may be placed in parallel with the dedicated ground
1
The induced voltage in this loop in the event of a magnet crash has been considered. It is sufficiently low, of order
10 mV for a 0.4 m radius loop at the worst-case ramp rate of 0.5 T / 30 s. Such a low voltage will not pose any
threat to the electronics and will not generate sufficient current in the thin copper foil ground plane of the FGT to
warrant concern about magnetic forces on the structure.
conductor. These ground conductors (1 per FEE and thus 4 per disk running together) serve as the
ground reference for the disk. They tie to the TPC structure ground immediately outside the WSC.
The cable type 1 has independent conductors for +1.8 power feed and return, and -1.8 power feed and
return, and sense lines for these. None of these are shared with the ground conductor.
A detailed listing of connections on each cable type is given later in this document.
From the patch point immediately outside WSC there are 24 power/sense cables (type 3 in the figure),
24 signal cables (type 4 in the figure), and 24 HV coaxial cables (type 4) running about 55 feet to rack
2C9. The reason for splitting the power/sense cables from the signal cables is simply due to
materials/construction: The signal cables require low dielectric loss which practically requires foam
polyethylene or foam teflon insulation. The power/sense cable is a custom construction with mixed wire
gauges to minimize diameter and mass in the constrained routing space over the TPC electronics. A
custom construction with polyethylene that would meet burn requirements would be expensive and
carry unpleasant schedule risk. Foam teflon is simply very expensive technology. So, we opt for a
commercial foam polyethylene cable carrying the required burn rating, and a custom PVC cable for the
power/sense connections.
Grounding scheme
As described in the following three sections. A diagram will be prepared but it should be fairly clear
already from this description.
Grounding scheme – at detector
Simply stated in three bullet points:



All signals and power connections are ground referenced to the ground at the detector. That is
to say, they have a low AC impedance to ground at the detector. The LVDS input signals and the
current-mode APV chip differential output signals have their common-mode level set at the
detector by a split resistor termination scheme.
The HV cable ground is isolated from the detector ground with a modest resistance (1 kΩ) safety
resistor.2 The HV center conductor is isolated with at least 1 MΩ, the primary purpose being to
protect the detector from stored energy in the cable and power supply.
The detector ground, as mentioned above, is carried in the power/signal cable on an
independent conductor out to the patch point.
Grounding scheme – patch point / ground reference
Here the ground conductor terminates to the TPC structure ground (west wheel) immediately outside
the WSC. Presumably the WSC structure will be grounded similarly.
The power/sense/signal cable shields all tie to ground at the patch point.
2
Which has 1 V drop at the maximum output current of the HV supply.
The other conductors (power, sense, signal, HV) are all isolated from ground at the patch point. This
includes the HV coax outer conductor – patch connectors (SHV) will be enclosed in insulated sleeving to
maintain ground isolation.
Grounding scheme – at the rack
The bullet points here:


All signal and power connections have a high common-mode impedance to ground at the rack.
o Signal lines are received by DC coupled active line receiver tolerant of ±3 V or more of
ground noise. Termination is differential only.
o LVDS signals (CLK & TRG) are transformer coupled.
o I2C signals are optically coupled
o Power is from low noise push-pull DC/DC converter with remote sense circuits powered
locally from the output. The complete set of 4 lines (power and return) taken together
has high common-mode impedance to ground.
The HV cable is ground referenced here at the power supply. This is ok because we isolated it at
the other side. Supplies with floating output are available but the cost is excessive and other
specifications are compromised a bit.
Inner signal cable (cable type 1)
The inner signal cable is a custom copper-clad aluminum construction per the following:
SPECIFICATION: Calmont Wire & Cable #3007-3397-02-10
36-Conductor Multi-Gage Shielded FEP/Silicone Special Purpose Cable.
8ea low voltage wire 22(1) Copper-clad Aluminum, FEP to nominal wall of .005". Color: Natural.
28ea signal wire 28(1) Copper-clad Aluminum, FEP to nominal wall of .007". Color: Natural.
Twist: signal wires into 14 matched impedance pairs (115-ohms ± 15%).
Overall: 1st layer, 8 ea. 22(1) CCA singles + 2 ea. unshielded twisted pairs of 28(1)
CCA cabled with fillers using LHL.
2nd layer, 12 ea. unshielded twisted pairs of 28(1) CCA cabled using RHL.
Shield: Aluminum-Mylar foil with 22(1) Copper-clad Aluminum drain wire (in contact with foil).
Jacket: Silicone, Yellow, Nominal wall of 0.020" and nominal OD of 0.299".
Note: Refer to drawing 3007-3397-02-10.
The conductor usage is per the following table:
wire 1
wire 2
wire 3
wire 4
wire 5
22 CCA
22 CCA
22 CCA
22 CCA
22 CCA
ground
+1.8 V force
-1.8 V force (note 2 parallel conductors)
-1.8 V force (note 2 parallel conductors)
return (i.e. 0 V) force
wire 6
wire 7
wire 8
pair 1
pair 2
pair 3
pair 4
pair 5
pair 6
pair 7
pair 8
pair 9
pair 10
pair 11
pair 12
pair 13
pair 14
drain wire
22 CCA
22 CCA
22 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
28 CCA
22 CCA
+1.8 sense
return (gnd) sense
-1.8 sense
SCK & VSS (I2C)
SDA & VSS (I2C)
TRG (LVDS)
CLK (LVDS)
APV 0 output (diff. analog
APV 1 output (diff. analog
APV 2 output (diff. analog
APV 3 output (diff. analog
APV 4 output (diff. analog
APV 5 output (diff. analog
APV 6 output (diff. analog
APV 7 output (diff. analog
APV 8 output (diff. analog
APV 9 output (diff. analog
ground (at patch point)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
HV cable (cable type 2)
This is same cable type is used from the detector (HVB) to the patch point, and from the patch point to
the rack.
The cable is equivalent to Draka P/N HTC-50-1-1,0.5Lz/1.5,CEH50, datasheet appended here. This is a
3.2 mm OD high voltage coax rated for 5 kV DC. The actual manufacturer and P/N vary; Doug Hasell of
MIT is responsible to get actual datasheets as required for safety approval.
Conductor usage as follows:
inner
outer
HV bias (0 to −5 kV)
ground
External power/sense cable (cable type 3)
This runs from the patch point to the rack, one cable per FEE group (24 total). Custom construction per
the following specification:
The conductor usage is per the following table:
wire 1
wire 2
wire 3
wire 4
pair 1
pair 2
pair 3
pair 4
drain wire
#18
#18
#18
#18
#24
#24
#24
#24
#20
+1.8 V force
-1.8 V force (note 2 parallel conductors)
-1.8 V force (note 2 parallel conductors)
return (i.e. 0 V) force
sense (+1.8 V & gnd sense)
sense (-1.8 V & gnd sense)
SCK & VSS (I2C)
SDA & VSS (I2C)
ground (at patch point)
External signal cable (cable type 4)
This is Belden # 1424A. Datasheet appended here. It is a 12 pair foam polyethylene cable with OD 0.418
inch.
Conductor usage is per the following table:
wire 1
pair 1
pair 2
#24
#24
#24
no connection
TRG (LVDS)
CLK (LVDS)
pair 3
pair 4
pair 5
pair 6
pair 7
pair 8
pair 9
pair 10
pair 11
pair 12
drain wire
#24
#24
#24
#24
#24
#24
#24
#24
#24
#24
#24
APV 0 output (diff. analog
APV 1 output (diff. analog
APV 2 output (diff. analog
APV 3 output (diff. analog
APV 4 output (diff. analog
APV 5 output (diff. analog
APV 6 output (diff. analog
APV 7 output (diff. analog
APV 8 output (diff. analog
APV 9 output (diff. analog
ground (at patch point)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
±4 mA)
Appendix (standard item datasheets)