Sensors and Alarms

Screens 6 and 2 display the status of a variety of sensors and warning alarms which may be modified by the user through the ALARM and SENSOR keywords.

The rationale behind computer-controlled sensors is that information obtained from some sources is critical to proper tracking and data-taking. If any of these sources fail, the programs should receive this information from an alternate source. The SENSOR command allows a defective sensor to be turned off and its information to be fed in by the user.

To turn a sensor off and inject a replacement value, one must type:
SENSOR (i.d.#) OFF (replacement value).
All four quantities must be present, even if a replacement value is unnecessary. To turn the sensor back on, type:
SENSOR (i.d.#) ON.

There may be up to a five minute delay between the time when a sensor is turned on and the time when the updated value appears. The on/off status is remembered from the last run when //STP is typed. All sensors are turned on when //ITP is typed. What follows is a listing of each sensor's i.d.# and its purpose:

Sensor 1

Universal Time
When on, UT is read from the station clock. Should that break down, the computer clock can be substituted by typing SENSOR 1 OFF (hhmmss) where the UT is entered for the moment when the SEND/ENTER key is pressed. This resets the computer clock to UT. For safety's sake, if the user employs this substitute, the computer time should be checked against WWV periodically, and the sequence SENSOR 1 OFF (hhmmss) should certainly be repeated each time the tracking programs are started up. The keyword CLKSET sets the computer clock to WWV time and then turns sensor 1 off.

Sensor 2 and 3

Electronic Level Corrections
These corrections are based on information supplied by the levels mounted on the telescope. Should the levels fail, or should the user not want the level corrections, typing either SENSOR 2 OFF 0 or SENSOR 3 OFF 0 will stop both level corrections from being applied to the pointing. Both sensors must be on for the level corrections to be applied.

Sensor 4

Outdoor Air Temperature
The air temperature recorded by a sensor mounted in the weather station is used in pointing corrections and is displayed as TAMB on screen 1. If this breaks, enter the replacement value in degrees Celsius.

Sensor 5

Radome Dewpoint Temperature

Sensor 6

Outdoor Dewpoint Temperature
This is used in refraction corrections for frequencies less than 100 GHz. The user can either replace this temperature in degrees C or just replace Sensor 8 below.

Sensor 7

Atmospheric Pressure
The replacement value should be entered in millibars.

Sensor 8

Water Vapor Pressure
This is really a pseudosensor, since the water vapor pressure is computed from the outdoor dewpoint temperature. One can directly replace the computer water vapor pressure in millibars using this sensor.

Sensor 9

Lock Indicator
This sensor reflects the radiometer phaselock loop and MM LO status and is important because data-taking will not proceed if this sensor is ON and the receiver is out of lock. Thus, is the receiver is unlocked but the user wishes to proceed with observations, type SENSOR 9 OFF 0.

Sensor 10

Total Power Monitor
The control radiometer DVM is read and used to determine if data-taking should proceed. To turn this off, type in a replacement value in millivolts.

Sensor 11

Function Buttons
When on, this sensor allows the use of the functions buttons FNA, FNB while in keyboard mode. When off, the functions buttons are ignored.

Sensor 12

Panel Switches
When this sensor is on, the panel digiswitches have their normal meaning. When off, the panel switches are disconnected from the tracking programs. This includes use of the digiswitches for manual fivepoints. Also, pointing offsets from the bottom row of digiswitches are no longer entered.

Sensor 13

Control Room Red Button
When this sensor is on, the "red button" for communicating with the tracking programs is enabled. When off, it is disabled, and the left-most console switch (bit d of the group of 16) on the computer replaces it (turn switch on briefly, then off).

Sensor 14

Platform Red Button
When sensor is on, the upstairs button is enabled. When off, it is disabled.

Sensor 15

VCO Lock
When enabled, this monitors part of the LO system.

Sensor 16

When enabled, the UT correction factor (UT1-UTC) is compute automatically at UT midnight. When disabled by tuning this sensor off (e.g., SENSOR 16 OFF 0.2), the UT correction factor is left at the values entered when the sensor was turned off. After the sensor is turned on again, automatic computations will begin at the next UT midnight, or at the next //STP startup, whichever comes first.

Sensor 17

Gunn Oscillator -
This sensor warns of an overheating condition in the 3 mm cooled mixer receiver.

Sensor 18

IF Chain
This sensor warns of an overheating condition in the 3 mm cooled mixer receiver.

The alarm status displayed on screen 6 allows the user to determine which warning alarms are on or off. All alarms are turned on automatically each time the tracking programs are started up. To turn an alarm off, type ALARM (i.d.#) OFF. To turn it back on, type ALARM (i.d.#) ON. Note that turning any alarm on or off has no effect on the condition that caused the alarm. All alarms may be turned off with ALARM ALL OFF and on with ALARM ALL ON. Some comments about the alarms follow:

Alarm 1

Subreflector Limit
If the commanded subreflector position (screws A, B, C) is outside physical limits, the subreflector does not move and the alarm goes off.

Alarm 2

Subreflector Error
If subreflector screws A, B, and C are more than 15 millivolts from the commanded position, the alarm sounds. The Y axis error is handled by alarm 9.

Alarm 3

Frequency Synthesizer Limit
If the computer synthesizer frequency is not within preset limits, nothing new is output to the synthesizer, and the alarm goes off.

Alarm 4

Azimuth Wrapup Limit
If the telescope gets within 40 of 0 or 720 , an alarm goes off and the computer halts the telescope if it is under computer control. The telescope must then by manually backed out.

Alarm 5

Lock Error
If the receiver drops out of lock and sensor 9 is on, the alarm goes off.

Alarm 6

Total Power Monitor
If the total power meter reading during an observation differs from its value at the start of the observation by more than a typed in tolerance [set by typing TPTOL (value in millivolts)], the alarm goes off.

Alarm 7

Level Error
When the difference between the expected level correction and the actual readout values exceeds a set tolerance, the warning sounds.

Alarm 8

VCO Lock
Warns if L.O. VCO is unlocked or locked.

Alarm 9

Y Axis Error
If the commanded Y axis position differs from the actual position by more than 15 millivolts, the alarm sounds. Also, if the commanded position is unreachable, an alarm goes off.

Alarm 10

Planet Tracking
If the planet tracking bombs, or if the user changes sources to a name which is not a solar system object, but fails to change both the MAIN and REF names, this alarm will go off. To clear, either restart planet tracking by reentering the solar system's object's name, or else change both the MAIN and REF names from the solar system object name.

Alarm 11

DVM Error
Goes off if the panel dvm overloads or fails to achieve a stable "read" status.

Alarm 12

SUBR DVM
If the subreflector position-sensing dvms overload or fail to achieve a stable "read" status, this alarm goes off.

Alarm 13

ENC ERR
If the AZ, EL position encoders fail to read properly, this alarm goes off.

Alarm 14

DOME HUM
If the radome dewpoint temperature equals or exceeds the outdoor air temperature, this alarm goes off, signaling a "POSSIBLE RADOME HUMIDITY PROBLEM".

Alarm 15

CLOK ERR
If the station clock jumps, this alarm will sound, and continue to sound until the alarm is turned off, then back on.

Alarm 16

Expander
If the spectrum expander signal level is out of range when F4 is in the current backend configuration, the alarm will go off.

Alarm 17

GUNN OSC
Warms of an overheating condition in the 3 mm cooled mixer receiver.

Alarm 18

IF CHAIN
Warns of an overheating condition in the 3 mm cooled receiver.

Alarm 19

LIQUID NITROGEN LEVEL

Alarm 20

POLARIZER POSITION
The polarizer can only function between angles 10 and 350 . Commanded values outside this range are not passed on to the polarizer. As long as the illegal value is commanded, the message will appear.