Pixel Cooling System Control

This page contains information concerning the control of the pixel cooling system (i.e. control groups, interfaces, etc.). Circuit mapping information can be found at PixelCoolingMapping.

A very brief summary of the following information, with figures, can be found here as a powerpoint file.

Introduction and System Layout

The pixel cooling system consists of 88 loops of the following breakdown:

• 56 Barrel Loops
• 24 Disk Loops
• 8 Opto Loops

These loops each have their own forward pressure and back pressure regulators. The regulators maintain pressure at a value given by an air pressure input. The entire system is controlled by a PLC that takes certain inputs from the pixel PVSS cooling project.

The regulators for the pixel system are housed in four cooling racks which are located on the HS structures next to the cavern walls. The racks are labeled Q1, Q2, Q3, and Q4, with locations at levels 1 and 8 of both the US and USA sides of the cavern.

While each pixel loop has its own regulators, each loop is NOT individually controlled. That is, anywhere between 2 and 23 circuits are ganged together and controlled with a single input setpoint.

This arrangement leads to problems if it doesn't provide the granularity needed to control the detector properly. Since the top of the detector will be significantly hotter than the bottom, for instance, it is necessary to be able to control the detector structures at the top of the volume independently from those at the bottom.

In addition, due to problems with the staves, there are three different types of bi-stave circuits in the pixel system:

• "New Bistaves" which have near to the originally designed cooling parameters
• "Single Inserted Bistaves" which have one "original" and 1 inserted stave (with significantly reduced pipe diameter)
• "Double Inserted Bistaves" which have two reduced-diameter, inserted staves

It is not yet known how many of each type will be present in the final detector, and it is important to be able to control the different types independently, at the least.

Current Control Groups

The current control scheme has the following characteristics, and is graphically illustrated in the following diagram, with a table of circuit counts following.

• There are 12 control groups overall
• There are 6 control groups in any individual rack (quadrant)
• The minimum number of circuits per group is 2 (opto circuits)
• The maximum number of circuits per group is 23 (L1-2 Bottom)

The current scheme has three problems:

• It provides a granularity that is too coarse in the barrel region (23 circuits are all controlled from one pressure setpoint)
• It does not allow for separate control of the different types of bi-staves, and their thermal performance will not be known until we are well into operation
• It divides disk circuits into "top" and "bottom", but the disk circuits span the x-z plane of the detector, so this division is either angled at 45 degrees or oddly grouped

Proposed Control Groups

The following proposed scheme rearranges the groupings into a more logical, more controllable, and safer design. It has the following characteristics:

• There are 12 control groups overall
• There are 7 control groups in any individual rack (quadrant)
• The minimum number of circuits per group is 4 (opto circuits)
• The maximum number of circuits per group is 14 (L2 Sides)

In effect, A to C side divisions have been removed, as there is little reason to suspect temperature deviation in Z. The control in the Y (vertical) direction has been increased, and L1 and L2 have been separated. In addition, a group at the bottom of L2 has been included in order to create a control group that will only contain double-inserted bistaves. This group may be expanded or reduced depending on how many double-inserted bistaves go into the final detector.

Summary

The proposed changes here do not result in a significant change to the cooling system overall, as there is a conservation of the total number of control circuits. This preserves the PVSS programming, the PLC programming, and possibly the hardware required. The mapping is unaffected, and the circuit destinations do not change. The one significant change is that instead of requiring 6 control groups at each rack, we now require 7. The implications of this increase must be understood before the change is finalized.

-- NealHartman - 01 May 2006