1993/03/10: Model 208 thermometer has been replaced by DRC-91
temperature controller.  These instructions are no longer needed.

This is a brief introduction to the operation of the model 208 cryogenic
thermometer as used with the SONIC.  The thermometer has two functions:
monitoring temperatures, which are stored with the data, and preventing
damage to the detector by too rapid heating.

There are four temperature sensors in use.  In order by channel, these
are: 1) control stage for SONIC detector, 2) detector block, 3) detector
chip, and 4) internal cold shield.  Channel 3 is uncalibrated and
normally read out in volts, while the other three are calibrated in
kelvins.

Normally the thermometer operates during the night under computer
control.  The computer cycles through the four channels and records the
temperatures in a log file.  It also records the most recent temperature
readings in each stored data file.

The thermometer may also operate under manual control, either monitoring
a single channel or scanning.  To operate manually, make sure the
computer program is not running, or disconnect the thermometer from the
computer by removing the telephone-type cable from the plug in back.
(Disconnecting the cable will kill the computer program if it was
running.)  Use the "channel" button to select channels individually.
(Channels 5-8 are not connected to anything.)  Holding the channel
button for more than one second (but less than two) will initiate a
continuously repeating scan of channels 1, 2, and 4.  A small light will
go on in the channel window to indicate that a scan is in progress.  You
can stop the scan by again holding the channel button down for more than
one second.  Temperature units may be changed freely with the "units"
button.

The thermometer also contains an alarm circuit, which is used to protect
the detector.  The alarm activates when channel 1 goes above 30 K.  If
the heater is plugged in through the thermometer, as it should be, alarm
activation will disconnect the heater.  This will protect the detector
from warming up too quickly if the cooler goes off for any reason.
Alarm activation is indicated by a small light in the upper left of the
temperature window.  The alarm will go off and the heater will go on
again when the temperature drops below 30 K.

IMPORTANT: 
In order for the alarm to protect the detector, the thermometer must
either be under computer control or set manually to channel 1.  DO NOT
LEAVE THE THERMOMETER IN SCAN MODE OR SET TO ANY OTHER CHANNEL.  Also,
make sure the heater is connected via the thermometer and not directly
to the electronics.