The CSO Weather sensor, related software, etc.

Introduction

The CSO's weather sensor is located inside the dome, on the third floor on the left hand side, about 3 feet away from the front. It measures temperature, barometric pressure and relative humidity. Its output goes into the antenna computer through an OP-Amp.

The weather information is used in the antenna computer itself to calculate refraction and to display on its monitor for information of the observers.

Two separate programs exist in the VAX to access weather information and to log it.

As we don't have an anemometer but do have wind speed limits for operation we usually use information from JCMT for this purpose.

The Weather Program

The weather program lives in the VAX. It is hardly used anymore these days because the weather information is displayed on the antenna computer's monitor. The weather program accesses the weather information in the antenna computer, which has to be running for it to work.

The Weather Log Program

The weather log program is a batch process running in the VAX. It has a lock on the antenna computer and for this reason will get stopped and restarted on antenna computer reloads. Weather information gets logged every 5 minutes to two ASCII files, one as the permanent log, the other one to be available on the world wide web.
At this time the weather log doesn't only start a new file at UT 0 hours but also every time it is restarted. Files get opened/created with their expected final size for a day's weather information, 21 blocks, to prevent unnecessary disk fragmentation.

Cross-calibration of Relative Humidity Readings

From time to time we cross-calibrate our humidity readings with those taken at the JCMT. The JCMT is close enough to the CSO to have more or less the same weather conditions, which is not the case for the other telescopes on Mauna Kea, and their weather sensor gets calibrated from time to time.

Cross-calibration is done by obtaining the weather data from JCMT and comparing readings taken during the same time intervals. The programs and procedures used in this sit in USER:[MAREN.UTIL.WEATHER.CAL].

CAL.COM takes one argument, the date, in form yymmdd. It then first runs FTPFILE which writes the ftp command file, then FTP, using the just produced command file, to transfer the required weather log over from JCMT. SEARCH is used the reduce the rather large JCMT weather log to something that doesn't contain a whole lot more than the time interval and the humidity readings. GREGFILE then takes the JCMT humidity file together with our own ones (JCMT are running on HST, so one file from one telescope will always require two from the other one) to produce a three column ASCII file that contains the time and the two humidity readings.

JCMT weather and log

The batch process that transfers JCMT's weather files to us on a regular basis runs in the Alpha. This was done because the Alpha is largely underused, the VAX has too many processes in it as it is, and this batch process doesn't need any access to micros. It can be restarted if necessary by logging into the Alpha and typing

@USER:[MAREN]START_JCMT_WEATHER_ALPHA_NOLOG

(it does sometimes hang or crash but this is rather rare).

This again is a DCL procedure that runs other procedures and programs, all of which can be found in $2$DKB0:[CSO.UTIL.WEATHER] (caveat: none of this works if the VAX and the Alpha aren't clustered right). It produces several output files each time it runs but purges them each time. The files of interest, and available both via DCL commands and on the world wide web, live in USER3:[HTML] and are called JCMT_WEATHER.DAT and JCMT.LOG. The DCL commands that display (type) them are JCMT_WEATHER and JCMT_LOG respectively.

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Maren Purves, maren@poliahu.submm.caltech.edu

Oct. 23, 1996