| CSIRO Astronomy and Space Science Parkes Users Guide |
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Should any problem arise after bussiness hours (4:30PM - 08:00AM) or on weekends, there is always one member of the technical staff who is the Call–out person. The name of the current staff member who is on call–out, together with their phone number, is prominently displayed in the first level control room and on the web(3). They can be contacted at any time out of normal working hours, in the event of a problem, by calling the abbreviated dialling code 633 (no leading 0), which reaches the Call–out mobile phone. A home phone number may also be listed. Call–out personnel will advise of the preferred means of contact. Should they be unable to answer your query by phone, they will come out to the telescope to have a closer look at the problem, or refer it to another staff member with more expertise in that area.
The essential elements of the Parkes RadioTelescope Control System are:
The disadvantage of an Alt-Azimuth mounting arises when tracking celestial objects across the sky, because the dish must move in two axes at varying rates, whereas an equatorial system moves only in one axis at the constant sidereal rate. When the telescope was designed in the 1950s, high speed computers capable of performing the rate calculations were not available. The problem was solved by the incorporation of a "Master Equatorial" (or ME) telescope. The ME is situated at the intersection of the Azimuth and Zenith axes and is mounted on a cylindrical column within the tower structure which is physically isolated from the tower. This has the added advantage that any movement in the tower structure which supports the dish does not affect the telescope system pointing. The ME tracks the object across the sky, and the dish follows by minimising the misalignment between it and the telescope by means of an Error Detector System.
The Error Detector is situated under a cylindrical cover in the hub room. It consists of a low power He-Ne laser and a circular array of light-detecting diodes. The laser is beamed towards a plane mirror in the top of the ME, and when the dish and the telescope are aligned to within one arc minute, the reflected beam falls on the detector diodes. The offset of the laser beam from the centre of the array is read by the servo computer which, when the offset (error) is below one minute of arc, closes the servo loop, causing the dish to accurately follow the movements of the telescope. The dish is then said to be "locked" to the ME. Only then can the telescope be driven in right ascension or declination. Errors during tracking and scanning are typically less than ten seconds of arc.
The maximum drive rate for the dish in Azimuth is 24 degrees/minute in either direction. The corresponding maximum Zenith rate is 10 degrees/minute downwards or 12 degrees/minute upwards. The maximum ME slew rates rarely are not normally of concern to an operator, but are close to 60 degrees/minute in both hour angle and declination.
Figure 4.1: Azimuth Drive Hardware and Software Limits.
In Zenith, the dish is limited to movements between 1.2 < Zenith < 59.5 degrees under normal software operating conditions. At 1.2 degrees, the dish enters its "Zenith limit", within which it can only be driven at a greatly reduced rate. A similar situation occurs when the dish approches the 59.5 degree mark. Similarly, the dish is not free to rotate in Azimuth indefinitely because of cabling constraints. As shown in fig:wrap, the "cable-neutral" position is at an Azimuth of 68 degrees. There are two hardware (software) limits, one at 294.66 (294.4) degrees and the other at 206.67 (207.0) degrees, and one is active at any time. The dish may not be driven through the active limit. If the dish enters one of these limits, special procedures are necessary to drive it out (see later).
Which limit is active is determined by the position of the dish with respect to the 68 degree mark. If the dish has entered the overlap region via the North direction (Azimuth = 0), it is said to be in a "North wrap" and this information is displayed on the bottom lefthand corner of the SHOWTEL monitoring program. Alternatively, if the dish has entered the overlap region from the South, it is said to be in "South wrap". For example, at 60 degrees, the 206-degree limit is active, whereas at 80 degrees the 294-degree limit is active. If the dish is in the overlap region, and the 206-degree LED is lit, this means that the overlapping region was entered from the North (a counter-clockwise drive). Therefore to observe a source with an Azimuth below 206 degrees a long clockwise drive would be required.
The ME also has limitations in both Hour Angle and Declination, but these will not normally be encountered because the ME is not normally driven directly. The one exception is if the ME has been left tracking for a long period with the dish stowed, when it will encounter the western hour angle limit.
The Translator is an electro-mechanical device used for positioning receiver packages at the focal point of the telescope. It has 5 axes of motion, namely:
Movement in any of these axes allows any of the installed receivers to be positioned at the telescope focus, and, optionally, to be maintained at the "best-focus" position during the observation, compensating for dish distortions. The translator can also be moved in the axial direction (parallel to the optical axis) to optimise or adjust focus. Rotation of receivers is also possible, typically to "parallactify" the feed (i.e. compensate for the relative rotation of the telescope focal plane on the plane of the sky, due to the Alt-Azimuth design of the telescope).
Schematics of the translator and focus cabine are shown in fig:translator and fig:focuscabin respectively. Typically, the larger receivers such as the 1050CM and 20CM Multibeam take up an entire mounting frame whereas smaller receivers such as the 13MM, GALAILEO, etc only take up half.
Figure 4.2: Layout the the translator
Figure 4.3: Cross sectional view of the focus cabin
The current system comprises the following computers;
Figure 4.4: The Master Control Panel and UPS alarm (upper right).
The 64m Master Control Panel (MCP) is the primary interface between the PDP11-23 Telescope Drive Computer (SERVO), the limit switches and sensors mounted on the telescope structure and the SWEO Regenerative DC Drives that control the motors. It provides interactive functions to bring the telescope into operation, position it manually and safely stow it when operations are complete. The Azimuth and Zenith drives are independent, and it is possible to drive the dish in one axis with the other axis still stowed.
A description of MCP features is presented below.
Figure 4.5: Sub–system LEDs on the MCP.
On the top right section of the MCP there are 24 pairs (one spare) of LEDs. fig:MCP_LEDS shows the layout. The following describes the condition of that part of the system if the LED is red.
The Operator is responsible for the safety of the telescope and must be able to carry out correct safety and emergency procedures to cope with all conditions. The Operator must monitor the weather at regular intervals. The SHOWTEL monitoring program, the VAISALA wind indicator and the WINDS program help in this task. VAISALA is the wind speed and direction indicator. This is a real time indicator interfaced to the SERVO computer to initiate an automatic wind park according to wind conditions. WINDS displays trends over the last hour. Every 120 seconds, the WINDS display is updated with a bar indicating the average and maximum (gust) wind velocities over the last 120 seconds. The OPERATOR is required to make outside weather inspections regularly and whenever a computer wind park occurs.
The SERVO computer monitors the speed and direction of the wind from
both Anemometers (one on the dish, the other in the paddock), and
will stow the dish automatically above limits defined in tab:wind_park
to ensure the safety of the telescope. These limits are monitored by SERVO
and can be displayed on the maintenance page on DISH0-PA (near the MCP) by
typing CTRL P M.
The (software) automatic stow must not be overridden. However, observers should be aware of the wind restrictions, and in the event that PKDESK has crashed they must be prepared to stow manually. In this situation the wind may be monitored from the wind indicator in SHOWTEL or by using WINDS on the VMS machine YOWIE.
The conditions (wind velocities; km/hr) under which the telescope automatically
stows are shown in tab:wind_park and can be monitored from the maintenance
page of the SERVO display on DISH0-PA (near the MCP; type
CTRL P M).
Peak Gust Average Ane #1 (Az front) 58 54 42 Ane #1 (Az front) 58 54 42 Ane #1 (Az back) 46 42 35 Ane #2 (Az front) 66 62 48 Ane #2 (Az back) 53 48 40 |
Table 4.1: Wind Park Algorithms
The Peak (2 consecutive readings), Gust (5 readings in the last 180), and Average (15 readings in the last 20) values (in km/hr) must be satisfied for a wind park to occur.
The “Az back” for each Anemometer are for winds within Azimuths 150 degrees < Az < 210 degrees (ie, winds within 30 degrees of the back of the telescope). The “Az front” values are for the remaining 300 degrees “front-on”sector.
The wind must be below the values given above for at least 10 minutes before the telescope can be unstowed. During a computer initiated wind park it is strictly forbidden to prevent it using the MCP drive controls! Once an automatic wind park has occurred, the telescope must not be unparked until permissible conditions have prevailed for at least 10 minutes. If conditions are poor, the telescope must be fully stowed.
During an automated wind-stow, the telescope drives to an Azimuth that has the wind at least 60-degrees away from the back of the dish without driving into an Azimuth limit. If you are observing near one of the limits and there is an easterly wind this could involve driving up to 100 or so degrees.
The wind has a greater effect on the Zenith motor currents of the dish
at high Zenith angles and if it is directed either towards the
surface or the back of the dish. The main problem is that a
strong wind onto the back of the dish can "hold it down" causing
the motor currents to reverse (the counter weight is heavier than
the dish). In this case, you might receive a ’HIGH/LO Current Stow’
(as reported by SHOWTEL). In a physical sense, the low current
condition is intended to detect overbalancing of the telescope
when a strong wind blows into the back of the dish. The threshold
for the low current condition is three occurances in 120 seconds
where the difference between the Zenith motor currents is -2.5 Amp.
Again, this can be monitored from the maintenance page of the
SERVO window on DISH0-PA (near the MCP; type CTRL P M).
Switch the MCP RATE SOURCE to "MANUAL".
Zenith:
Azimuth:
Once completing the above AND you are leaving the telescope vacant, press the red POWER "OFF" button (NOTE: this disables the Safety Timer as well, as does disabling both Azimuth and Zenith drives when stowed.)
Azimuth:
Zenith:
When fully unstowed, except for "Remote Control" and "Azimuth Wrap" LEDs, all other LEDs should also be green.
The trouble is most likely caused by wind pressure pushing a pair of jacks at an uneven angle, not allowing enough room to rotate the jacks. By rotating the antenna in Azimuth, you take the pressure of one pair of jacks and share it onto two pairs. If you are attempting to put the telescope onto jacks in high winds and you can’t turn one of the jack levers around :
The Observatory has two sources of power. The principal power supply is provided from the 11kV Country Energy mains. A 250kV diesel generator provides a backup supply to most circuits in the tower (and some elsewhere on site) in the event of mains failure. Some critical circuits have a further backup from a UPS (Uninterruptible Power Supply) which can last up to 1 hour, supplying ctitical systems. Computers, electronics, clocks, masers and receiver systems are connected to the UPS protected circuits. The lights, telescope drives and many other systems are not protected by the UPS.
There is also a timer high on the wall of the first level control room (see Figure fig:mainsfail_indicator; above the WINDS and SHOWTEL displays) which shows the time since the last interruption to the mains supply. If the mains supply is available, the timer will be updating. If there is no mains supply to the Observatory, the timer display will be all zeros and the small red mains-failure lamp will be illuminated.
Figure 4.6: Timer in control room showing time since last power failure.
If the Country Energy mains fail, the generator should start automatically and provide power so that after a short interruption you will be able to resume observing. The actions you will need to take are described in detail in Resetting the UPS Alarm.
If the generator fails to start and the mains supply does not return (the room lights in the control rooms go off and stay off, this is a CRITICAL situation and must be dealt with IMMEDIATELY, as described in Severe Power Failure - no mains or generator.
You can monitor the Mains and GenSet with Monica (Monica) by clicking on Parkes - Navigator - favourites - generators. Monica should be running on the third or fourth-screen on bourbon in the control room (or you can install using the link above). A screenshot of the generators display is below.
Figure 4.7: The Parkes generator monitor page in Monica.
The likely scenarios are dealt with separately below.
As of August 2009, the MCP no longer disables itself during a Power Failure. A power outage of sufficient length will disable the SWEO drives and apply the brakes, but the MCP will remain in computer control. If the outage is only a glitch of a few 10s of milliseconds - just enough to flash the lights but short enough for the SWEO drives to stay on - the telescope drive will continue as if nothing happened.
When the outage is long enough for the SWEOs to be disabled - e.g. when the generator starts or stops - the drives will be disabled and the brakes applied. Once the power is stable the drives may be re-enabled while the MCP remains under computer control. If the dish is still in lock capture range of the ME the telescope will reacquire lock and the drive can resume.
During any interruption, an alrm will sound in the control room indicating you will need to reset the UPS alarm beside the MCP, as described in Resetting the UPS Alarm. On the Monica display display, you should see the following:
If there is a failure of the mains for longer than a second, the generator should start automatically. Once it is up to speed it will be switched to supply the telescope. The interruption to the supply will trigger an alarm to sound next to the MCP (see Resetting the UPS Alarm), and the mains interruption timer will be reset to zero and will not update. To recommence observing it will be necessary to enable both the azimuth and zenith drives, and switch back to computer control.
On the Monica display display, you should see the following:
If both of these items are false, this indicates an ERERGENCY SITUATION and must be dealt with IMMEDIATELY, as described in Severe Power Failure - no mains or generator.
When the mains power is available again, and has been stable for a period of around 1 minute, the suppy will automatically revert from generator to mains. The MCP will remain on and because the generator synchronises with the mains on transfer back to mains power, it happens without a break, so the UPS suffers no break in input power. This means that the alarm panel near the MCP will not enter an alarm state at this time.
This is a CRITICAL situation and must be dealt with IMMEDIATELY.
If the mains power fails and does not return, and the generator fails to start or stops for some reason, you must immediately intervene. The best indicator of this situation is that the room lights in the control rooms will go off. If they stay off for more than 30 seconds or so then the only source of power is the UPS and urgent action is required. Another indicator of this situation is the timer high on the wall of the first-level control room displays all zeros and does not update.
Note: The phone system in the tower has its own UPS which will last for approximately 1 hour. After that, the only operational phone will be the one in the first level control room on the centre column labelled Emergency Phone.
The emergency phone has the following features.
If there is a need to pre–empt a main outage (Thunderstorms, planned maintenance), you will need to go to the generator hut. Once there, put some ear muffs on (located in silver cabinet outside generator hut) and proceed inside to the left of the generator where you will see the control panel for the generator as shown below in fig:genset_control.
Figure 4.8: Generator Control Panel.
Figure 4.9: Switch for transfering power to/from Mains/Generator.
To manually switch over to the generator, move the "POWER SOURCE SELECTION (local)" switch, see fig:genset_maingen, to "GEN". Once this is done, the generator will start and bring itself up to speed so the changeover from Mains to generator can occur.
When you decide to switch back to Mains, go back over to the generator hut and switch the "POWER SOURCE SELECTION (local) switch from "GEN" to "MAINS".
Note: It is no longer necessary to halt observing to switch between the Mains and the generator.
If the power from the generator should fail in some way, the system will automatically switch back to mains power.
In the event of a power outage, an alarm in the control room (see fig:UPS_1stfloor) will sound indicating the UPS alarm next to the MCP needs to be reset.
Figure 4.10: UPS alarm in the control room.
To reset the UPS alarm beside the MCP (see fig:UPS_alarm), perform the following:
Figure 4.11: UPS alarms on the first and second–floor control rooms.
This document was generated by Stacy Mader on October 13, 2011 using texi2html 1.82.
