Impedance Monitor

Impedance Monitor M. Utes 19-July-2016

Impedance Monitor: • Ground Isolation Impedance Monitor (GIZMo) • Monitors the integrity of a particle detector’s isolation from building components.

Particle Detectors Components of the D-Zero detector

DzeroDetector Calorimeter, Toroid, Muon Chambers MUON CHAMBERS TOROID CALORIMETER ELECTRONICS RACKS

DzeroDetector • Electronics racks in lower Platform

CDF Detector • Exploded view of CDF

MicroBoone Neutrino Detector • First day in the experimental hall for MicroBoone

Particle Detectors- What they consist of: • Particle detectors consist of different detector types, each with many channels. Wire chambers, drift chambers, calorimeters, silicon strip detectors. • Sensitive electronics • Small analog signals, digital signals/clocks • Single-ended and differential copper signals, optical signals • Power supplies often with large currents • Cooling fans, cryogenics • Common mode noise of D-Zero Silicon Detector was 10µV

Particle Detectors- Grounding for low noise and safety • Modern detectors- usually large devices • Star (single point) ground technique • Low impedance copper ground grid • Whole detector isolated from building ground except for • Single safety ground • Saturable inductor in safety ground path

Saturable Inductor • 10-turns 2AWG around 12-mil Selectron STL

Saturable Inductor • Impedance vs. Frequency

Saturable Inductor • Impedance vs. Current showing core saturation

Particle Detectors- Grounding for low noise and safety • It’s important to maintain ground isolation throughout the duration of detector assembly • If a rogue connection is made, many man hours can be spent looking for multiple shorts.

Single-point Detector Ground • Need to establish and maintain detector isolation during assembly with safety ground attached

Impedance Monitor Location IPCT OUTPUT STIMULUS CURRENT INTEGRATED PARAMETRIC CURRENT TRANSFORMER * IPCT outputs 1 Volt per mA

Impedance Monitor Installed • Shown near transformer and load center • This view shows IPCT in bypass configuration IMPEDANCE TRANSFORMER IPCT IPCT

Impedance Monitor • Close-up of Bypass Box in monitoring configuration WIRE TO GND IPCT STIMULUS WIRE WIRE TO DETECTOR

How it works • Sends AC or DC current through current transformer to detector. • Ideally, all current travels back to Impedance Monitor through current transformer via safety GND. • Currents cancel and current transformer outputs no signal • If a rogue path to GND exists, it will steal some of the current away and complete cancellation in the CT will not occur. • CT output is proportional to the impedance of the short

How it works • Sends AC or DC current through current transformer to detector. • Ideally, all current travels back to Impedance Monitor through current transformer via safety GND. • Currents cancel and current transformer outputs no signal • If a rogue path to GND exists, it will steal some of the current away and complete cancellation in the CT will not occur. • CT output is proportional to the impedance of the short • Alarm occurs if CT output goes above a preset threshold

Block Diagram

Safety Aspects • Detector safety ground must always be maintained • Proper bypass procedure must be followed • “Operational Readiness” Inspection • Equivalency memo (Electrical AHJ approval)

Concrete Cell In one application, GIZMo was saturated even though apparent isolation existed…. The detector rested on concrete Concrete is not a good insulator. In fact, it can make a battery

Next generation Gizmocould employ Lock-In Amplifier • Lock in amplifier works at only one precise frequency and exhibits high signal to noise ratio CRYOSTAT SINE X IPCT UNWANTED CONNECTION LPF BUILDINGGROUND

Summary • Impedance Monitor monitors violations of GND isolation in real time • Real time audio alarm • Remote monitoring capability

Impedance Monitor