Ancillary Controls for the Cooling System:
Sensor Failure Issues

The MVD consists of two identical halves (east-west). Therefore all power and cooling is split this way, and all interlocks address at most only one half of the MVD at a time (the exception is failure of the humidity control sytem, which affects both halves). The MVD can still gather data with one half when the other half is down.

These tables are for sensor failure only. They assume that the safety/interlocks presented in the general fault charts are in operation.



Unified Air Cooling System Sensors

Failing sensor

Capabilities of that sensor

Means of diagnosing or double checking

Consequences of failure
The humidity sensor Talk only--no automated shutdown under any circumstances No direct double check; there is only one humidity sensor. The time between signals from the liquid level sensor is humidity-related and may help. We would have to run system uncontrolled or go in to fix the sensor. High humidity could affect the placement of the detectors, requiring changes in vertex finding algorithms.
A flowmeter (one of 3) Hardware shutdown if 2 out of 3 report trouble There are 3 flowmeters such that F1 = F2 + F3. If one fails, we can fill in its measurements using easy math. If another also fails, we can't.
One MCM temp sensor fails Eventual software shutdown (algorithm undetermined--probably shut down in blocks of six MCMs) Can check MCM above/below that one in flowstream; if there is a discrepancy, ignore the failing temp sensor from then on. Also can check signal to noise ratio for the affected MCM. One temp sensor doesn't work and can't be used for measurements or to double check another sensor.
Liquid level sensor Controls a valve that drains water out of loop If average time between signals is recorded, can sense deviation from normal schedule. Can also keep draining system at intervals in the absence of signals from the sensor. The draining of water from the dehumidifier will be less controlled.
Temp sensors in the flow loop Hardware shutdown if 2 out of 3 report trouble Temp sensors in the loop should have some correlation between readouts. Any one failure is okay, but system has one less doublecheck.

FC-75 liquid cooling system sensors

Failing sensor

Capabilities of that sensor

Means of diagnosing or double checking

Consequences of failure
Temp sensor in flow loop (one of 2) Hardware shutdown with flow sensor (F7 and T8, F8 and T10)

Hardware shutdown if both temp sensors report trouble

 Temp sensors on motherboard, and requiring both to show trouble before shutdown. Can still control with only one working. Less redundancy in liquid system control; if T8 or T10 goes town, the flowmeter will be able to act alone.
Flowmeter Hardware shutdown with temp sensor (F7 and T8, F8 and T10) No direct backup; only one flowmeter. Temp sensors double check to some degree. Pump would have to run uncontrolled, and system could not directly detect leaks in the liquid loop
Motherboard temp sensors (one of 3) Software shutdown (algorithm undetermined) As with MCMs, make sure they agree As with MCMs, there's one fewer temp sensor for measurement and double checking.

This page last modified on 7 September '98 by Rachel Cunningham.