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AUSTRALIAN
NATIONAL UNIVERSITY System Design Note 10.00 Created: 6 April 2000 Last modified: 6 April 2000 |
NIFS INSTRUMENT CONTROL SYSTEM OVERVIEW
Martin Mulligan
Research School of Astronomy
and Astrophysics
Institute of Advanced
Studies
Australian National
University
Revision History
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Revision No. |
Author & Date |
Approval & Date |
Description |
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Revision 1 |
Martin Mulligan 20 September 1999 |
Jan van Harmelen 05 April 2000 |
Original document. |
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Revision 2 |
Peter J. McGregor 05 April 2000 |
Jan van Harmelen 06 April 2000 |
Reformatted for Word 2000. Updated following CoDR. |
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Contents
4 Instrument
Control System (ICS)
5 Optical
Component Controller (OCC) Electronics
5.1.1 Rotary
Positioned Elements
5.1.2 Linear
Positioned Elements
5.2 Summary
of Motors, Magnets, & Sensors
6.1.1
Temperature Regulation Hardware
6.2 Control
of Cryo-Cooler During Cool-Down
6.2.1
Cryostat Cool-Down Hardware
6.3 Control
of Cryostat Heaters During Warm-Up
6.3.2 Auto-Shutdown and Inter-Lock Safety System
6.3.3
Cryostat Warm-Up Hardware
1 Purpose
The purpose of this document is to provide an overview of the Instrument Control Systems (ICS) to be used in the Gemini Near-infrared Integral-Field Spectrograph (NIFS). In particular, this document focuses on the Optical Component Controller (OCC) and Thermal Controller (TC). These are the two main control systems associated with the NIFS cryostat. The design of the NIFS ICS will be copied to the largest extent possible from the ICS for NIRI, the Gemini Near Infrared Imager. NIRI has been designed and constructed by the Institute for Astronomy (IfA) of the University of Hawaii. Control of the NIFS science detector system and the NIFS On-Instrument Wave Front Sensor (OIWFS) detector system are not covered within the scope of this document.
2 Applicable Documents
|
Document
ID |
Source |
Title |
|
HI96822 |
IfA, UH |
Gemini NIRI Critical Design Review |
|
SPIE, Vol. 3354 |
IfA, UH |
Design of a Cryogenic Wheel Mechanism for IRCS and NIRI |
|
niri_hty_002/03 |
IfA, UH |
Near IR Imager (NIRI) – Detailed Design Document |
|
GNIRS SDN0012 |
NOAO |
GNIRS Electronics Design |
|
ICD-13/04 |
IGPO |
Gemini Controls Group Interface Document |
|
|
|
|
3 Introduction
The Gemini
Near-infrared Integral-Field Spectrograph (NIFS) is a complex arrangement of
optical elements, filter wheels, gratings, mirrors, and sensors which need to
be thermally controlled as well as moved and aligned with great precision in
order to ensure maximum scientific performance and versatility. It is the function
of the Instrument Control System (ICS) to control all of these operations thus
leaving the detector controllers unfettered. Broadly speaking, the ICS may be
thought of as two separate control systems operating under the same VME single
board controller.
·
The Optical
Component Controller (OCC) and the
·
Temperature
Controller (TC).
Both of these control
systems are described in general terms in this document.
The NIFS ICS will be
largely a copy of the ICS used with NIRI, the Gemini Near Infrared Imager. NIRI has been designed and constructed by
the Institute for Astronomy (IfA) of the University of Hawaii. This document
describes the operation of the NIRI control mechanisms in the NIFS context, and
also highlights areas where the NIFS control system will differ from that used
in NIRI. A schematic of the NIRI ICS is shown in Figure
1.
Figure 1: Schematic of the NIRI Instrument Control System.
4 Instrument Control System (ICS)
A VME single board computer controls the operation of the ICS. This computer is interfaced to the VME backplane via a transition module which provides industry standard connectors to the computer.
4.1 ICS Hardware
1´ Motorola MVME167-033B Single Board Computer.
33 MHz, 16 Mb ECC DRAM, full 32-bit master/slave VMEbus interface, DMA VMEbus D64, SCSI interface, Ethernet interface, quad EIA-232-D serial ports, 8-bit bi-directional Centronics parallel port, four 32-bit timers, watchdog timer, 8 Kb of NVRAM with real time clock/calendar, remote Reset/Abort/Status control.
1´ MVME712 I/O Transition Module.
Four DB25 serial ports, Ethernet port, SCSI port, printer port via P2
adapter board, power status LEDs.
1´ Datum Inc. BC635VME Time and Frequency
processor board.
100 ns accuracy real time clock from time code signals, typically IRIG
B.
5 Optical Component Controller (OCC) Electronics
The Optical Component
Controller (OCC) is responsible for moving and positioning all of the optical
elements associated with the NIFS cryostat. Within the cryostat there are two
major sub-systems, the On-Instrument Wave-Front Sensor (OIWFS) and the NIFS
spectrograph. Externally, there is also a light-tight cover for the cryostat
window.
The NIFS OCC will
control and position the following seven active elements:
|
·
OIWFS X-Axis
Gimbal |
linear positioned |
|
·
OIWFS Y-Axis
Gimbal |
linear positioned |
|
·
OIWFS Filter
Wheel |
rotary positioned |
|
·
Spectrograph
Focal Plane Mask Wheel |
rotary positioned |
|
·
Spectrograph
Order Blocking Filter Wheel |
rotary positioned |
|
·
Spectrograph
Grating Wheel |
rotary positioned |
|
·
Environmental
Cover |
open/closed |
5.1 Control Strategy
The NIFS active
elements will mostly be controlled using copies of NIRI mechanisms. An open
loop scheme using stepper motors and dead reckoning is employed using Hall
effect sensors to provide "home" or "datum" positions. Once
a zero-point is established, the number of steps taken by the stepper motor
determines position.
Hall effect sensors
consist of a small block of semiconductor material, such as indium, sandwiched
between two metal electrodes. A weak DC voltage is produced between these
electrodes in the presence of a magnetic field. This voltage is typically ~ 10
millivolts per kilogauss. The polarity of the potential difference is a
function of the "pole orientation" of the magnet field (north-seeking
or south-seeking).
The position
monitoring and calibration system will use stationary Hall effect sensors and
small position-indicating magnets mounted on specific moving parts of all
stepper motor driven optical component mechanisms. Additional (redundant) Hall
effect sensors, which are software selectable, are included to improve
reliability.
All movable elements
within the NIFS cryostat can be categorized as either rotary or linear
positioned.
5.1.1 Rotary Positioned Elements
The OIWFS Filter
Wheel, Spectrograph Focal Plane Mask Wheel, Spectrograph Order Blocking Filter
Wheel, and Spectrograph Grating Wheel are rotary positioned elements.
All rotary elements
are positioned absolutely by a detent system, and driven by a modified “Geneva Drive” (Figure 2). “Home” position is determined by a single
magnet and Hall effect sensor. The magnet is mounted on the rim of the wheel
and passes perpendicularly under the stationary Hall effect sensor.
Figure 2:
Modified Geneva Drive with a locking detent pin.
The output from the
Hall effect sensor, as the magnet passes under it, rises to a peak as more
magnetic flux passes through the area of the Hall effect sensor and then
declines again as the magnet moves away (Figure 3). Figure 4 shows how the Hall effect sensor output varies in
relation to the steps of the stepper motor.
The “Home” position is
found by finding the midpoint between two points of identical magnetic flux
(i.e., output voltage from the Hall effect sensor). This should provide a high
level of repeatability and be tolerant to sensor sensitivity and DC drifts or
offsets introduced by the Hall effect sensor amplifiers.
Figure 3:
Hall effect sensor output vs radial angle.
Figure 4:
Hall effect sensor output vs stepper motor steps.
Redundancy can be
provided by placing another Hall effect sensor in parallel with the first, but
rather than mounting it on top of the primary it is placed to the side on a
slightly smaller radius. This provides a two track system which creates a
quasi-positioning system which, with the inclusion of some additional magnets
of variable field strengths, provides an absolute code for each filter or
grating position. If two magnets are used, each with two different field
strengths, up to 16 positions can be encoded absolutely (Table 1). The largest wheel in NIFS has 8 positions.
Table 1: Two Magnet/Two Track Encoding System.
|
Primary Track |
Secondary Track |
Position |
|
N1 |
N1 |
Home |
|
N1 |
N2 |
N/A |
|
N1 |
S1 |
N/A |
|
N1 |
S2 |
N/A |
|
N2 |
N1 |
N/A |
|
N2 |
N2 |
N/A |
|
N2 |
S1 |
N/A |
|
N2 |
S2 |
N/A |
|
S1 |
N1 |
Position 1 |
|
S1 |
N2 |
Position 2 |
|
S1 |
S1 |
Position 3 |
|
S1 |
S2 |
Position 4 |
|
S2 |
N1 |
Position 5 |
|
S2 |
N2 |
Position 6 |
|
S2 |
S1 |
Position 7 |
|
S2 |
S2 |
Position 8 |
If we choose to make
the “Home” position the only position which employs a north-seeking magnet in
the primary track, it should speed up finding the “Home” magnet pair. There
will most likely be some offset between the absolute position of primary “Home”
and secondary “Home” which must be determined empirically.
The position
indicating magnets will be Samarium Cobalt rod shaped magnets, which produce a
magnetic field intensity of approximately one kilogauss. Intensity will be
controlled by adjusting the depth of the mounting hole.
Being rotary systems
there is no need for limit switches or hard stops to prevent excess travel.
5.1.2 Linear Positioned Elements
The OIWFS X-Axis
Gimbal, and OIWFS Y-Axis Gimbal, are linear positioned elements.
Both linear positioned
elements move back and forth on lead screws over a finite travel distance.
Position is determined by a combination of Hall effect sensors and magnets (Figure 5). Coarse position is determined by measuring the flux
between a North-South pair of magnets and fine position is determined by
measuring the rotary position of the lead screw in a method similar to that
detailed in §5.1.1.
The coarse positioning
or “linear” magnets are placed with opposite polarities, producing two adjacent
peaks, one positive the other negative. Between the peaks, there is a ramp,
which is (almost) linear (Figure 6). This stage is designed so that it is always
operated in the linear region, providing a useful although not extremely
accurate encoding of the position stage. Note that any changes in the
sensitivity of the sensor electronics or DC offset can affect this encoding
scheme. This is sufficient, because the encoding scheme needs only to position
the stage datum to within one turn of the main gear. A zero-crossing comparator
is provided to rapidly find the “Coarse Home” position, This is the point in
the middle of the two magnets where the Hall effect output crosses from
negative to positive or visa versa.
Figure 5: Encoding scheme for linear positioned
elements.
Figure 6:
Linear element Hall effect sensor output vs position.
Fine positioning is
determined by measuring the rotary position of the lead screw in a method
similar to that detailed in §5.1.1. A single magnet and Hall effect sensor pair will be
used to seek the peak response while travelling outwards from the “Coarse Home”
position. Backlash in the gears is avoided by travelling in only one direction.
This lead screw peak position is used as the “Home” or “Datum” position for all
further screw displacements (Figure 7).
Figure 7: “Coarse Home” and “Datum” positions for linear positioned elements.
Multiple positions for
a single magnet will be milled into the lead screw spur gear so the choice of
“Home” position may be made to provide the most versatile “Home” position in
relationship to the “Coarse Home” which may move slightly due to DC drift. This
must be determined empirically.
For redundancy, all
Hall effect sensors will operate in pairs, mounted in parallel with a software
switch choosing between primary or backup sensor. Should one Hall effect sensor
fail, the computer will switch to the backup sensor. There will be a slight
difference in peak position because it is not possible to ensure that the
sensors are concentric with each other. This must be compensated for in
software. The magnitude of compensation will be determined empirically.
No provision is made
for backup limit switches or hard stops to limit linear travel. Limit switches
have a high rate of failure in cryogenic conditions so were deemed unsuitable
for NIRI and it was thought that the current system of using backup Hall effect
sensors was reliable enough so that hard stops were unnecessary. The operation
of this system in NIRI will be monitored.
5.1.3
Open/Closed Elements
The Environmental Cover is an open/closed element.
The Environmental Cover is unique in operation in NIFS; it has only two relevant positions, “Open” or “Closed”. The cover is a two vane sliding cover, driven by a flexible belt with limit switches signaling the end of travel (Figure 8).
Figure 8: Environmental Cover assembly drawing.
In the “Closed” position, the cover should be light tight and protect the cryostat window from dirt, dust, and moisture likely to be encountered during storage or shipping. In the “Open” position during operation, the cover should be retracted and provide an unobstructed path for light to enter the cryostat.
An Ionizer Sprayer Head (item 14 in Figure 8) is separate to the mechanism for opening and closing the Environmental Cover but part of the same sub-assembly. This head is responsible for venting de-ionized, dry, non-turbulent air over the cryostat window in order to prevent moisture condensing during astronomical observations.
A Cleaning Spray Bar (item 8 in Figure 8), is also part of the Environmental Cover sub-assembly. It uses a high pressure jets of dry air to clean the lower vane and cryostat window of large detritus. The air from this jet is highly turbulent and will not normally be vented during astronomical exposures.
5.2 Summary of Motors, Magnets, & Sensors
|
Assembly |
Sub-Assembly |
Details |
Part |
Qty |
|
OIWFS |
Gimbal X-Axis |
20 mm Worm |
Cryogenic Stepper Motor |
1 |
|
|
|
X-Motion Screw Travel Position |
Hall Effect Sensor |
1 |
|
|
|
X-Motion Screw Travel Position
– Backup |
Hall Effect Sensor |
1 |
|
|
|
X-Motion Motor Position |
Hall Effect Sensor |
1 |
|
|
|
X-Motion Motor Position –
Backup |
Hall Effect Sensor |
1 |
|
|
|
Lead Screw linear position |
Samarium Cobalt Magnet |
2 |
|
|
|
Spur Gear rotary position |
Samarium Cobalt Magnet |
1 |
|
|
|
|
|
|
|
OIWFS |
Gimbal Y-Axis |
20 mm Worm |
Cryogenic Stepper Motor |
1 |
|
|
|
Y-Motion Screw Travel Position |
Hall Effect Sensor |
1 |
|
|
|
Y-Motion Screw Travel Position
– Backup |
Hall Effect Sensor |
1 |
|
|
|
Y-Motion Motor Position |
Hall Effect Sensor |
1 |
|
|
|
Y-Motion Motor Position –
Backup |
Hall Effect Sensor |
1 |
|
|
|
Lead Screw linear position |
Samarium Cobalt Magnet |
2 |
|
|
|
Spur Gear rotary position |
Samarium Cobalt Magnet |
1 |
|
|
|
|
|
|
|
OIWFS |
Filter Wheel |
6 Position Geneva Drive |
Cryogenic Stepper Motor |
1 |
|
|
|
Track 1 (Datum) |
Hall Effect Sensor |
1 |
|
|
|
Track 2 & Backup |
Hall Effect Sensor |
1 |
|
|
|
Track 1 |
Samarium Cobalt Magnet |
1+6 |
|
|
|
Track 2 |
Samarium Cobalt Magnet |
1+6 |
|
|
|
|
|
|
|
Spectrograph |
Focal Plane Mask Wheel |
6 Position Geneva Drive |
Cryogenic Stepper Motor |
1 |
|
|
|
Track 1 |
Hall Effect Sensor |
1 |
|
|
|
Track 2 & Backup |
Hall Effect Sensor |
1 |
|
|
|
Track 1 |
Samarium Cobalt Magnet |
1+6 |
|
|
|
Track 2 |
Samarium Cobalt Magnet |
1+6 |
|
|
|
|
|
|
|
Spectrograph |
Order Blocking Filter Wheel |
8 Position Geneva Drive |
Cryogenic Stepper Motor |
1 |
|
|
|
Track 1 |
Hall Effect Sensor |
1 |
|
|
|
Track 2 & Backup |
Hall Effect Sensor |
1 |
|
|
|
Track 1 |
Samarium Cobalt Magnet |
1+8 |
|
|
|
Track 2 |
Samarium Cobalt Magnet |
1+8 |
|
|
|
|
|
|
|
Spectrograph |
Grating Wheel |
6 Position Geneva Drive |
Cryogenic Stepper Motor |
1 |
|
|
|
Track 1 |
Hall Effect Sensor |
1 |
|
|
|
Track 2 & Backup |
Hall Effect Sensor |
1 |
|
|
|
Track 1 |
Samarium Cobalt Magnet |
1+6 |
|
|
|
Track 2 |
Samarium Cobalt Magnet |
1+6 |
|
|
|
|
|
|
|
Cryostat |
Window Cover |
Open/Closed |
Stepper Motor |
1 |
|
|
|
End of travel sensors |
Microswitch |
2 |
|
|
|
Ionizer |
|
1 |
5.3
OCC Hardware
Stepper Motors:
8´ Phytron VSS 52 200 1.2 UHVC - (52 mm outside
diameter, 200 steps/revolution, 1.2 Amps /winding), 405 mNm torque, -270 C to
+40 C, 10-11 Torr.
1´ Phytron ZSS 52 200 1.2 - (52 mm outside
diameter, 200 steps/revolution, 1.2 Amps /winding), 405 mNm torque, -120 C to
120 C.
Bipolar Stepper Motor Power Stages:
9´ Phytron ZSO MINI 42-40, 4 A peak phase
current, 0.6-2.3 A effective, 24V-80V supply.
TBD ´ Power Stage Racks SLS-ZSO, IP 115 Vac, houses
1-6 ZSO power stages.
1x Kepco Power Supply RAX 48-30K, 1500 W (IP
90-132 Vac or 180-264 Vac, OP 48 V, 30 A).
Alternatively, 9´ Phytron SINCOS-L, ±8 V to ±21 V supply.
Alternatively, 1´ SINCOS Power Supply TBD.
VME Bus Stepper Motor Controllers:
2´ Oregon Micro Systems, VME8-8; note this unit
is now obsolete and may have to be replaced by the following or similar units:
Alternative 1´ Oregon Micro Systems, VME58-8, 8 Axis Control, 0 feedback, 5 Vdc @ 1.75 A from VME
Bus.
Alternative 1´ Oregon Micro Systems, VME58-2, 2 Axis Control,
0 feedback, 5 Vdc @ 1.75 A from VME Bus.
Magnets:
75´ Jobmax Samarium
Cobalt Magnets,
2.5 mm diameter, 4 mm thick.
Hall Effect Sensors:
28´ F.W.Bell. FH-301-040, Transverse Hall Effect
Sensor, 12 mV/kG, 15 mA excitation. -55 C to 100 C.
Alternatively, 28´ Cryomagnetics HSU-1 Unpackaged, 5 mV/kG, 20 mA
excitation. -270 C to 30 C
Sensor Support Boards:
2´ Custom made PCB's (by IfA), 6U style, each
board containing:
6´ zero-crossing comparators.
14´ 15 mA constant current sources, depending on
sensor used.
14´ Instrumentation amplifiers, Burr-Brown
INA141's G=100.
1´ Power Supply OP ±12 V TBD.
Analogue-to-Digital conversion:
1´ XYCOM Inc. XVME-566 100 KHz 32-channel 12 bit
A/D Module, Supply ±5 Vdc 2.1 A from VME Bus.
Digital I/O Board:
1´ XYCOM Inc. XVME-240 64-channel bi-directional
TTL I/O, Supply +5 Vdc 2.7 A from VME Bus.
Ionizer:
1´ SIMCO Ionizer bar.
6 Temperature Controller (TC)
The Temperature Controller is responsible for:
· Temperature regulation.
· Control during cool-down.
· Control during warm-up.
6.1 Temperature Regulation
The NIFS cryostat consists of three main thermal sub-assemblies;
·
The OIWFS
detector.
·
The Science
detector.
·
The Cold Plate
thermal mass.
In NIRI, each thermal sub-assembly is regulated by its own Omega CYC321
Temperature Controller. The Omega CYC321 Temperature Controller is a 25 W PID
closed-loop controller incorporating silicon diode temperature sensors
operating over a range of 1.4 K to 475 K to an accuracy of ±0.1 K. Temperature set-point, heater On/Off,
curve data, and output data may be controlled over a RS232 link via a XYCOM
XVME-400 Serial I/O board located in the OCC VME Crate (Crate #1).
The NIFS science detector may require temperature regulation to ±1 mK. It is proposed to replace the science
detector Omega CYC321 Temperature Controller with a dedicated Lakeshore Model
340 dual temperature controller. It will be necessary to use both channels to
control the temperature of an intermediate thermal mass, as well as that of the
science detector thermal mass, in order to achieve the required temperature
regulation.
Since the output power of the CYC321 temperature controller is limited
to 25 W, additional power-boosting amplification is required for the Cold Plate
Thermal Mass heater sub-system. This is accomplished by converting the output
of the temperature controller to an analog voltage which is used to control a
200 W Kepco HSM 48-21 Remote Analog Programmable Power Supply.
Additional thermistors will be mounted at various locations within the
cryostat for use by the Accelerated Warm-up System. Preamplifiers for these
thermistors are located on the same board as the Hall effect sensor
preamplifiers. The amplified thermistor signals are connected to inputs on the
XYCOM Inc. XVME566, High Performance Analogue Input Modules, which are located
in the OCC VME Crate (Crate #1).
The OCC will also have a computer-independent Auto-shutdown and
Inter-lock Safety System to prevent overheating of cryostat parts should any of
the normal accelerated warm-up systems fail. This is described in §6.3.2.
6.1.1
Temperature Regulation
Hardware
Temperature
Controllers:
3´ Omega CYC321-01 Silicon Diode Cryogenic Autotune Temperature
Controllers. 110 Vac IP.
2´ Omega CYC320-HTR, 25 W Cartridge Heater.
1´ 200 W Resistor for cold plate.
3´ 1N914 diodes, good to about 50 K.
Alternatively 2x Lakeshore Model 340 Dual temperature controllers with
2´ Lakeshore Cernox RTD temperature sensors, Calibrated 20K-325K.
Analog Power Supply
for cold plate heater power boost:
1´ Kepco HSM 48-21 Remote Analog Programmable Power Supply, 1000 W,
100-250 Vac IP.
RS232 Serial
Controller:
1´ XYCOM Inc. XVME-400 Quad Serial I/O Board.
Sensor Support Boards
- used to monitor auxiliary temperature sensors:
1´ Custom made PCB's, 6U style, each board
containing
6´ Zero-crossing comparators
14´ 15 mA constant current sources, depending on
sensor used.
14´ Instumentational amplifiers, Burr-Brown
INA141's G=100.
Power comes from Supply OP ±12V used by Hall Effect Sensor Support Boards.
Miscellaneous cables
etc.
Remote Analog Programmable
Power Supply.
6.2 Control of Cryo-Cooler During Cool-Down
NIRI uses two Leybold Coolpower 130 Cryocoolers, but it is not clear
whether these are still available. Cooling of the NIRI cryostat is via cold
straps to internal mechanisms. Varying the motor speed within each cryo-head
regulates the rate of cooling. During normal cool-down operation, the speed of
the cryo-cooler will be set at 140 rpm, which is the factory recommended
nominal operating speed. During emergency cool-down operation only (minimum
cool-down time), the speed will be set to 200 rpm. Once a nominal cryostat
operating temperature has been achieved, the speed of the cryo-cooler will be
reduced to a value consistent with normal operation heat-load requirements. It
is estimated that reducing the cryo-cooler speed to about 30% of maximum would
be a nominal operating speed. The actual value will be determined during NIRI
commissioning.
Heater sub-systems will be used to control heat flow such that the OIWFS
and science detectors are always maintained at a slightly positive temperature
differential with respect to their surrounding environments in order to
minimize sublimation of any residual matter onto the detector surfaces.
The first stage of the cryo-head, which has the greater refrigeration
capacity, is cold strapped to the Cold Plate Thermal Mass and the second stage,
which can achieve a lower temperature, is cold strapped to the spectrograph
detector. The OIWFS detector is cooled by a cold strap to the Cold Plate
Thermal Mass.
6.2.1
Cryostat Cool-Down
Hardware
Cryo-coolers:
2´ Leybold Coolpower 130 Cryocoolers, 15 W at 20
K, 15 W, 115 W at 77 K.
Helium Compressor:
1´ Leybold Coolpak UCC 110S, 3-phase, 460 V, 60 Hz, 4-wire Delta with
motor drive electronics.
Motor Power Stage:
2´ 6410 Driver as part of the Leybold Coolpak UCC 110S compressor.
RS232 Serial
Controller:
1´ XYCOM Inc. XVME-400 Quad Serial I/O Board
(spare channel from Temperature Regulation Board).
6.3 Control of Cryostat Heaters During Warm-Up
Warming of the NIFS cryostat may be accomplished by turning off the
cryo-coolers and raising the set point of the thermal regulation system (§6.1). The normal Cold Plate Thermal Mass heater
sub-system will supply up to 200 W to the cold plate and 25 W to each detector.
6.3.1 Accelerated Warm-Up
Accelerated warm-up is possible by diverting power normally dedicated to
the stepper motors and the cryo-cooler motors to additional heater resistors
located on the Cold Plate Thermal Mass. An additional 800 W will become
available to provide the accelerated warm-up. Typical locations for these
additional heater resistors are the cold plate and charcoal getters.
The OCC CPU controls the temperatures of the cold-plate work-surface and
the detector thermal masses during the accelerated warm-up operation so that
positive detector temperature differentials are maintained to prevent detector
contamination.
During accelerated warm-up operation, up to one kilowatt of power will
be applied to the NIFS cold surfaces under the control of the OCC Heater
System. The OCC utilises the computer-independent Auto-shutdown and Inter-lock
Safety System to prevent overheating of critical cryostat parts should any of
the accelerated warm-up systems fail.
6.3.2 Auto-Shutdown and Inter-Lock Safety System
The OCC will utilize the computer-independent Auto-shutdown and
Inter-lock Safety System to prevent overheating of critical cryostat parts
should any of the accelerated warm-up systems fail.
The Inter-lock Safety System will:
1. Prevent accidental turn-on of the high power
heater system.
2. Require periodic “human verification” that
cryostat temperatures are within normal limits.
3. Automatically shut-down the high power heater
system if an UPS power failure should occur which could affect the accelerated
warm-up operation.
4. Automatically shut-down the high power heater
system if cryostat temperatures exceed 40 C (100 F).
5. Provide a computer-independent temperature
display of cryostat temperatures so that a human being can verify nominal warm-up
operation.
During accelerated warm-up, the Auto-shutdown System has the ability to
disconnect the 110 V to the power supply powering the cryostat heaters. Thermal
switches, located inside the NIFS cryostat, will trigger the shutdown. The
Auto-shutdown System will also be equipped with a timer that must be
periodically reset in order to continue the warm-up operation. This part of the
Auto-shutdown System will terminate the warm-up operation should weather
conditions prevent observatory access. Additionally, a reliable temperature
monitoring meter will be provided so that crew personnel can visually check the
cryostat temperatures.
Initiation of the accelerated warm-up operation will require active
human action. To start an accelerated warm-up operation, the following must be
accomplished:
1.
A panel
circuit-breaker has been set.
2.
A panel timer has
been set.
3.
All cryostat
thermostat switches are below 40 C (100 F).
4.
A panel
spring-loaded normally-off key-switch has been momentarily switched on.
5.
UPS and telescope
mains power are present.
6.3.3
Cryostat Warm-Up
Hardware
Heater Resistor:
Resistors selected for 800 W accelerated warm-up.
Panel mounted
temperature monitor:
Panel Mounted Thermal Safety circuits:
Resetable Watchdog
timer:
110 V solid state relay:
Accelerated Warm-up
power switch.
7 Sensor Support Boards
These custom made printed circuit boards (PCB's) are functionally identical to the Sensor Support Boards used in NIRI for interfacing with both Hall effect sensors and temperature sensing thermistors.
Custom made PCB's, 6U style, each board
containing:
6´ Zero-crossing comparators.
14´ 15 mA constant current sources.
14´ Instumentational amplifiers, Burr-Brown
INA141's G=100.
The output of these
amplifiers will be connected to two XYCOM Inc. XVME566, High Performance
Analogue Input Modules (12-bit A/D Converter). The pre-amplifier gain will be
set at 100 and the ADC full-scale digitization range will be ±0.25 V.
8 Divergence from NIRI
In essence, the operation of all mechanisms within NIFS is identical to NIRI with the following exceptions;
· If necessary, replacing obsolete Oregon Micro Systems, VME8-8 stepper motor controllers with newer Oregon Micro Systems, VME58-8 or similar stepper motor controllers.
· If found necessary because of interference, replacing the Phytron ZSO MINI 42-40, stepper motor power stage with Phytron SINCOS-L mini-step linear power stages. The SINCOS-L power stages are about the same cost but have reduced electronic interference. This change would require redesign of wiring, adding to system cost.
· If the SINCOS-L power stages are used, it will also be necessary to change from the Kepco Power Supply with its 48 V output to a ±8 V to ±21 V supply compatible with the SINCOS-L linear power stages.
·
Replacing the one
Omega CYC321-01 temperature controller with a Lakeshore Model 340 dual
temperature controller and also replacing the silicon diode temperature sensors
with Cernox RTD temperature sensors. This will provide the improved temperature
control required for the spectrograph detector.
Appendix A: List of Figures
|
Figure 1 |
niriblk2.bmp |
|
Figure 2 |
geneva drive.bmp |
|
Figure 3 |
rotary output vs angle.bmp |
|
Figure 4 |
rotary output vs steps.bmp |
|
Figure 5 |
linear stage.bmp |
|
Figure 6 |
linear sensor output.bmp |
|
Figure 7 |
linear sensor output – detailed.bmp |
|
Figure 8 |
cover.bmp |
|
|
|