SDN0012

SYSTEM DESIGN NOTE

SDN0012 - Electronics Design

Prepared by	Date	Approved by	Date	Rev.	Rev Date
Andy Rudeen	5/6/99	N. Gaughan	5/6/99

1.0 Introduction

This document describes the overall configuration and philosophy of the GNIRS Electronics controls. It also covers details of the mechanism (component) control and electronics packaging.

1.1 Electronics Overall System Configuration

The GNIRS Electronics conform to Gemini instrumentation standards and consists of 3 separately designed entities:

1) ALADDIN Array Controller (Section 2.0)
2) OIWFS Controller (Section 3.0)
3) GNIRS Components Controller (Section 4.0)

The overall GNIRS control architecture is shown in the block diagram below:

Figure 1. GNIRS Overall Control Block Diagram

2.0 ALADDIN Array Controller

The ALADDIN ARRAY Controller has been built by NOAO under a separate Gemini contract, and its design details will not be discussed here. It is housed in a standard Gemini-furnished Thermal Enclosure (TE). Its interconnections to the GNIRS dewar and the Gemini telescope are shown at:

ftp://ftp.noao.edu/gnirs/elect/5025.pdf

The ALADDIN controller also includes a separate preamp module which resides on the dewar and connects directly to the ALADDIN array as well as to the ALADDIN controller located in the thermal enclosure. For additional information on the ALADDIN controller refer to the following Gemini ICD’s:

1.9.1/1.9.2 Science Instrument Components to Detector Controller ICD

1.9.2/1.9.3 Detector to Detector Controller (InSb) ICD

3.0 OIWFS Controller

The GNIRS On-Instrument Wavefront Sensor controller is being provided by the Univ. of Hawaii's Institute for Astronomy (IfA). It is a copy of the OIWFS being designed for NIRI, and its design details will not be described here. The OIWFS controller package will be integrated into the GNIRS Components Controller Thermal Enclosure (CCO) and its packaging details are included in the discussion of that Thermal Enclosure below. The OIWFS system also includes a dewar-mounted controller box (the SDSU2 NIR array controller) which will be actively cooled via an integral commercially procured cooling plate.

4.0 GNIRS Components Controller

4.1 Overall Functions

The GNIRS Components Controller (CCO) electronics provide the following control functions:

    1)    control of the positioning of the cold GNIRS drive mechanisms
    2)    control of the positioning of the GNIRS external environmental cover
    3)    control of cryo-coolers
    4)    dewar temperature sensing
    5)    dewar vacuum sensing
    6)    remote dewar warmup control box

Temperature monitoring and control associated with the two detectors in the instrument are provided by their respective controllers and are not a function of the CCO. Note also that at present time there is no requirement for active control of the temperature of the instrument structure, although it will be monitored and temperatures deviating from a nominal range will be flagged by the instrument control software.

4.1.1 Motion Control Functions

NOAO is planning to use internal (cryogenic) stepper motors to drive the 9 GNIRS instrument cold mechanisms. Motor qualification is in process and will entail the selection, preparation, testing, and usage of a stepper motor for the approximately 60 degree Kelvin vacuum environment of GNIRS. These motors will be driven "open-loop" from accurately registered home position microswitches with custom mechanical triggering hardware. Limit switches sensing end-of-travel will be incorporated into mechanisms with linear or rotary "range of travel" limitations. These limit switches will be redundantly wired to the stepper drive amplifiers as well as to the VME stepper indexer boards in order to provide motion stoppage at the level of the stepper driver hardware.

The selection of microstepping type motor drivers is planned for efficiency and smoothness of motor operation, although the mechanism drives will be designed to rely only upon the full motor step resolution. Stepper motor control electronics will provide the function of powering off stepper motors when not in use, then turning power on again without loss of the original position. The GNIRS environmental cover is a warm external mechanism and will also use a stepper motor, and microswitches to sense in and out positions.

Motor drive electronics and power supplies will be sized to accommodate altitude derating and simultaneous operation of all GNIRS mechanisms. It will also be designed to provide sufficient torque and operating speed for the stepper motors based upon mechanism drive and instrument operational requirements. The capability for programmable drive current settings (2 settings only) for the stepper motors will also be included in the design. Drive currents are set with externally changeable resistors which are wired into the driver units.

4.1.2 Cryocooler Control

The CCO will provide control of the operation of the GNIRS cryocoolers. These will be commercial Leybold units with either DC stepper motor (model #130), or AC synchronous stepper motor (model #5/100) heads. There are currently no plans to incorporate any electronic phasing of the multiple (2 or 4) cryoheads, although the usage of the Model #130 head would lend itself to VME software control of the motor STEP pulses as it would be driven with the standard mechanism VME motor controller board.

4.1.3 Dewar Vacuum Sensing

The CCO will provide vacuum sensing capabilities for the GNIRS dewar. The vacuum sensing will be performed using a commercial VARIAN gauge controller housed in the TE that communicates via a serial RS232 interface to the CCO host VME CPU board. All vacuum gauges will only be powered during readback.

4.1.4 Dewar Temperature Sensing and Thermal Control

The readback of temperature sensing diodes in the GNIRS dewar will be performed by a custom-designed NOAO VME card that also provides diode excitation via a multiplexer circuit that leaves the diodes in a normally unpowered state. This board allows for 27 channels of diode readback. Plans are to install 27 diodes for general purpose instrument thermal sensing with the possibility of additional diodes being installed for diagnostic purposes. The diodes will be of the 1N914 variety except if used at the coldhead stages where lower temperature (30-40K) are attained. These areas would use Lakeshore diodes that are more accurate at low temperatures (1N914 diodes become non-linear below about 50 degrees Kelvin).

The ALADDIN and OIWFS arrays have their own separate thermal control and temperature readback capabilities. There are currently no plans for the GNIRS control system to provide active thermal control of the GNIRS dewar and internal structure or mechanisms.

4.1.5 Remote Warmup Controller Box

A manually operated dewar warmup heater control box will be designed which will provides manual control of the GNIRS dewar warmup resistance heaters. This will be a "standalone" box that incorporates a commercial process controller unit and appropriate temp sense diode excitation, and voltage readback scaling circuitry. The power source for warmup heating will be wall AC power that is switched ON/OFF by the process controller to achieve the desired warmup ramp profile. The total wattage and type of resistive heater elements (pads or discrete resistors) is to be determined pending further instrument thermal studies.

4.2 CCO Hardware Configuration

The GNIRS Components Controller and OIWFS Controller are housed in a second standard Gemini-issued Thermal Enclosure. This thermal enclosure is partitioned into 4 removable crates as shown in Figure 2:

Figure 2: GNIRS CCO Thermal Enclosure Layout

It will consist of the following crates from bottom to top of the TE:

    1)    One (1) 4U OIWFS Motor Driver Crate (Crate #1)
    2)    One (1) 3U Mechanism and Cryohead Motor Driver Crate (Crate #2)
    3)    One (1) 9U VME chassis, split backplane with 12 and 8 slots (Crate #3)
    4)    One (1) 4U Ancillary Control Electronics Crate (Crate #4)

4.2.1 OIWFS Motor Driver Crate

This will be delivered by the IfA, and will be a commercially procured 4U Phytron #SLS-4-ZSO MINI stepper motor driver crate designed for mounting in a standard 19" rack. It will contain 4 PHYTRON #ZSO 42-20 stepper driver modules and a self-contained power supply with fans. This unit will input the OIWFS VME stepper motor driver board's indexing logic, and output high level PWM motor phase currents to the 4 OIWFS-related motors.

4.2.2 Mechanism and Cryohead Motor Driver Crate

This will be a custom-designed 3U motor driver crate that accepts 12 axis of stepper motor indexing signals from the 3 CCO mechanism VME stepper boards, and outputs 10 axis of stepper motor high level PWM phase currents to the GNIRS mechanism motors. It will contain discrete DC power supplies for the motor drivers. Preliminary selection is for the use of small-profile CENTENT #CN0142 microstepping motor drivers, and bulk unregulated linear DC power supplies such as the Acopian Series U supplies for driver power (approximately +40V @12A total capacity). Unregulated bulk supplies can be somewhat bulky, but have high output capacitance and are ideal for handling the dynamic load requirements of stepper motors. The GNIRS mechanism motor load requirements are small enough to allow for their usage. This chassis will also contain simple custom-designed printed circuit mounting boards locating the current set resistors, optoisolators, hardware limit switch logic, and test points which interface to the CENTENT drive modules.

The crate will also contain the cryohead motor drive electronics. The exact configuration depends upon the head selection, as noted in Section 4.1.2 above. Preliminary drawings and chassis layouts plan for the usage of the bulkier DC controls for the Model #130 cryohead. If the AC head is used, the control circuitry will be much smaller and easily packaged into this 19" crate.

4.2.3 CCO VME Electronics Crate (Crate #3).

The 9U VME Electronics Crate will be a commercially procured crate from Systems Int. Plus in Scottsdale, AZ. It is specified as:

#SIP-98-AUR-C04, type 12 rackmount chassis, 9Ux20", split
12/8 slot VMEbus J1/J2 backplane, 60mm recess, hinged front,
rear transition area, and 750W top-mount power supply unit.

It features 2 separately bussed backplanes to allow housing the OIWFS and GNIRS Mechanism VME control systems in the same chassis as both controllers will have their own CPU boards. While duplicating some board functionality, this allows for easier integration of the 2 control systems and was baselined early on in the original GNIRS design process.

4.2.3.1 GNIRS CC VME Boards

The 12-slot GNIRS Components Controller VME backplane will house the following 7 Boards in slots #1 thru 12 facing the chassis:

1. One (1) Motorola MVME167-033B Single Board Computer
2. One (1) Custom NOAO 27-channel Temp Diode Excitation and Readback card
3-5. Three (3) Oregon Microsystems VME44-4 Intelligent Stepper Motor Controllers, quad channel with encoder feedback
6. One (1) Oregon Microsystems VME44-4 Intelligent Stepper Motor Controllers, quad channel with encoder feedback
7. One (1) XYCOM Inc. XVME-240, Digital Input/Output Module

Control interconnections to these boards can be seen in the drawing at:

ftp://ftp.noao.edu/gnirs/elect/5020.pdf

The CC and OIWFS VME CPU board connections will wire out to the standard connections of #MVME712 transition modules mounted in the rear transition area of the VME chassis. This transition area will also be populated by connector panels that provide for standard circular or D-type connectors interfacing cabling from the VME chassis backplane to other TE crates or the outside of the TE.

4.2.3.2 OIWFS VME Boards

The 8-slot OIWFS VME backplane will house the following 7 Boards in slots #1 thru 7 facing the chassis:

1. One (1) Motorola MVME167-033B Single Board Computer
2. One (1) Datum Inc. BC635VME Time and Frequency Processor Board
3. One (1) Oregon Microsystems VME8-8 Intelligent Stepper Motor Controllers
4-5. Two (2) Hall Effect Sensor and Thermistor Support Preamplifier boards (designed and built by IfA)
6. Two (2) XYCOM Inc. XVME-566, High Performance Analogue Input Modules
7. One (1) XYCOM Inc. XVME-240, Digital Input/Output Module

Design details will be described in IfA OIWFS documentation.

4.2.4 Ancillary Control Electronics Crate

This 4U custom designed chassis will house 3 "black box" units:

1. OIWFS - Omega Model CYC321 Temperature Controller, size = 8.5" H x 3.5" W x 12.5" D
2. OIWFS - SDSU2 "Leach" Power Supply, size = 9"D x 8"W x 4.5 H
3. CC - Vacuum Controller Unit, Varian Vacuum Gauge Controller, #CC2c, senTorr Gauge Controller,

contains 3 gauges which sense high vacuum (10**-9 torr), and 2 "ConvecTorr" low vacuum sensors
(1x10**-3 torr). Size = 3.5" H x 8.0" W x 15" D.

4.3 CCO TE Power, Grounding and Weight

Details of AC/MAINS power and GROUND usage as well as estimated weights of the CCO TE crates are shown in drawing:

ftp://ftp.noao.edu/gnirs/elect/5011.pdf

Chassis layouts will maintain careful isolation of the clean UPS GROUND used for sensitive detector electronics from the noisy MAINS ground used for motor power and other similar functions. This may entail the physical mechanical isolation of commercial rackmounted chassis hardware in the 19" rack system.

5.0 Connector and Cabling Summary and Philosophy

An overall GNIRS external connector and cabling summary can also be seen in the drawing:

ftp://ftp.noao.edu/gnirs/elect/5025.pdf

The general connector usage on the TE's and dewar will be circular MIL-SPEC type connectors unless noted.

Internal TE cabling will provide for demountable interconnect cables from the rear panel of the TE to the rear areas of the control and VME crates. These interconnect cables will have a sufficient service loop to enable pulling out the control crates from the front area of the TE for diagnostic purposes. The rear panels of the internal crates will have circular or D-type connectors to transition signals to fragile VME backplane or ribbon type connectors.

Cryogenic wiring will be carefully designed to minimize heat flow into the vacuum dewar, and also to provide thermal isolation between cryogenic components and outside dewar hermetic connectors.