Chapter 1 - NTT Electronics

1.1 INTRODUCTION

The NTT Electronics consists of several subsystems. Each subsystem has been built around a local computer (VME). The descriptive chapters are organized in the same way, by subsystem. However, several electronic units have no direct relation to a VME computer and cannot be classified under a VME system. This chapter gives descriptions of the NTT electronics in general and of electronic systems which are not directly related to a specific VME computer.

1.1.1 Reference Information

The following sections give specific information:

• Section 1.2 gives a general description how the abbreviation of all the computer I/O signals in the NTT are organized.
  Section 1.3 gives the assignment of the slipring contacts. This slipring is a part of the hydraulic joint mounted in the pillar of NTT.
  Section 1.4 describes the VME power supplies. Also provides information related to P2 connector Analog and Digital signal assignments.
  Section 1.5 provides a list of drawings and data sheets, and other maintenance information.
  

1.2 NTT SIGNALS

This section introduces naming conventions for the NTT signals connected to a VME computer. For each signal, an abbreviation is defined that is used in the hardware drawings and software.

1.2.1 Abbreviations

The abbreviations are defined as follows:

• Two characters to define the VME computer, which is the same as the Ethernet node. For example AZ for azimuth.
  Two characters generally to define the main subgroup. For example PA for power amplifier.
  The rest of the abbreviation (up to a maximum of 10 characters) to define the signal.

The following VME systems have been defined:

• AA: Adapter on fork arm A
  AB: Adapter on fork arm B
  AL: Altitude
  AZ: Azimuth
  BU: Building
  CA: Console A
  CB: Console B
  GA: Guider (autoguider + crosshair) on fork arm A
  GB: Guider (autoguider + crosshair) on fork arm B
  HB: Hydrostatic bearing
  M1: Mirror 1
  M2: Mirror 2
  M3: Mirror 3
  RA: Rotator on fork arm A
  RB: Rotator on fork arm B

The signals of each VME system are described in separate chapters. However, some VME systems are combined in one chapter: AA and AB, AL and AZ, CA and CB, GA and GB, RA and RB. This is done because the systems are identical. This structure provides easy access and maintenance. Another field in the description defines the type of the signal:

• DI*n:Digital input; n bits
  DO*n: Digital output; n bits
  AI*n: Analogue input; n significant bits
  AO*n: Analogue output; n significant bits

1.2.2 Level Convention

The defined level of the digital signals refers to the level at the digital I/0 board connection. There are however; "high true" and "low true" signals: "low true" signals are indicated with an asterisk(*) in the abbreviation.

The definition "asserted" (= "true") and "negated" (="false") always refers to the description of the signal: it is not concerned with voltage level.

1.3 SLIPRING

All electrical signals from the rotating building to the fixed ground are connected via a slipring. The slipring has a capacity of 64 signals. For each signal, a shield is available up to the slipring at both sides, but this shield is not connected through the slipring.

1.3.1 Video Driver/Receiver

One video signal can be taken from the rotating part of the NTT to the fixed part via the slipring. The 75 Ohm, asymmetric video signal is buffered close to the slipring by the video driver unit. This driver generates symmetrical (+ and -) video outputs which are fed to the rotating side of the slipring. On the fixed side of the slipring, the differential signal is received by the video receiver and transferred into a 75 Ohm asymmetric signal again, equivalent to the driver input signal. The two units must be installed within 1 meter distance from the slipring in order to minimize reflections. The whole chain is DC coupled.

1.3.2 Assignment

1.3.3 Remarks

The weather data, which was also entered via the slipring in the previous design, now enters the system via the VME rack of the hydrostatic bearing.

1.3.4 Drawing List

1.4 VME BOARDS

The VME boards which are used in the NTT local computers are commercial boards. For detailed technical information on each VME board, please refer to the corresponding manual.

1.4.1 Power Supplies

There are two possible power supplies, depending on the power required by the VME system:

• ELBA power supplies. In this case there are 2 power supplies: 5V/40A (type ESP81540) and + and -12V/4A (type ESP82153).
  LK power supply LKP3151. In this case there is 1 power supply which provides the three voltages. This supply has no sense lines and therefore, the 5V must be adjusted. This can be done by modification of R29 inside the power supply. A correct voltage on the VME backplane is achieved with R29=14k7. Because this modification is necessary, the LK supplies should not be used for new designs.

1.4.2 P2 Connector Analog signal assignments

48 ANALOG TO DIGITAL INPUTS. 2 DIGITAL TO ANALOG OUTPUTS

1.4.3 P2 Connector Digital signal assignments

AVME9481 DIGITAL I/O BOARD

1.5 GENERAL MAINTENANCE INFORMATION

This section contains the index of maintenance information for the NTT electronic units which are not related to any VME system. Some units are described separately, together with the drawings and maintenance information.

1.5.1 Interlocks

Some interlock conditions on certain subsystems have consequences for other subsystems as well. The following subsystem interconnections referring to interlocks are defined:

• From the hydrostatic bearing to azimuth in case of a fatal error in the hydrostatic bearing system.
  From the building to azimuth in case of an over-large angular difference between building and azimuth mechanical structures.

In order to prevent electromagnetic interference from one subsystem to the other, all these signals are coupled via relays.

1.5.2 Emergency Stop

The emergency stop push buttons are located at various points in the NTT. One contact of each of them generates a computer signal to a VME computer located in the area. The second contact of all the push buttons is connected in a chain, which de-energizes a relay in the azimuth power rack when a button is pressed. Note that power for this relay is also derived from the azimuth power rack.

The subsystems which are interlocked by emergency stop are defined:

• Azimuth
  Altitude.
  Building (rotation only).
  Rotator A.
  Rotator B.

In case of an emergency stop, a computer signal is asserted in all of these subsystems, indicating that a button (any button) has been pressed. The azimuth power rack and the building control VME rack act as two major junction points in the emergency stop wiring, see the emergency stop cabling diagram (CS-E-1613). This is done to limit the cabling and to give easy access for trouble shooting.

1.5.3 Ethernet Cabling

The Ethernet cabling is split into 3 "segments"; see the Ethernet Wiring diagram. The segments are connected via a "multi port connector"; which allows a star type of distribution instead of a daisy chain. The segments are split such that the cable length is minimized and additional nodes can be easily added.

Below, the main specifications referring to the cable are summarized. For a complete specification, refer to the book: "Local Area Networks, supplements to Carrier Sense Multiple Access with Collision Detection". The version used for NTT is type 10BASE2, which means 10 megabit/sec speed, base band modulation and RG58 type cabling with BNC connectors.

Summarized Cable Specifications:

• Segment length: <185 meter.Characteristic impedance: 50 +/- 2 Ohm.
  Attenuation: <8.5 dB over a 185 meter installed cable, measured at 10 MHz.Velocity of propagation:>0.65 c.
  Cable DC loop resistance: <50 milliOhm/meter.Total segment DC loop resistance: <10 Ohm.Grounding: the shield of the cable must be grounded at 1 point.
  Notes:
  The installation of NTT has been done with a RG58 type cable which has 0.66c propagation speed, e.g. BELDEN 8259. This cable has a transparent isolation, as opposed to e.g. BELDEN 8219. The latter type has 0.78c propagation speed and thus fulfills the specs. However, it is highly recommended to install future extensions with BELDEN 8259 or a similar type cable, first because of consistency and second because of the availability of correctly fitting BNC crimp connectors.
  The grounding of the total Ethernet cable installation is done in the slipring. There, the shield of the coax cable is connected to chassis ground. In the multi port connector, the shields of all segments are connected together, but they are not connected to chassis ground.

1.5.4 Drawing List

1.5.5 Hardware Boards