The Hardware

The PULPO 2 CPU board (see Fig. 2) is a Eurocard-size board. The core component is a credit card sized embedded PC module from Compulab. It hosts a complete PC with 486 processor, integrated 16 MB flash disk, 32 MB of RAM, Ethernet controller and all standard PC peripherals (serials, parallel port, IDE controller, etc).

Figure 2. PULPO 2 CPU Board.

PULPO 2 is supplied with +24V from the FIERA [5] linear power supply. All internal voltages (+5V, +3.3V, ±15V and +12V) are generated on the CPU board by means of DC/DC converters. Each voltage has auto-resetting SMD fuses. Standard bypassing plus additional PI filters are used to smoothen the supply voltages. A voltage supervisor, MAX814, on the 5 V supply is used to generate a reset on power-up and in the case of power failure. The MAX814 also provides the option of a manual reset via a button on the front panel. A 3V lithium battery with 3 years lifetime is used to keep the RTC (Real Time Clock) on the 486Core running in case of a power failure.

The RS232-to-fiber interface is built around a ML4624 chip. It drives an Agilent HFBR 1414 transmitter and receives commands via a HFBR 2416 receiver. The fiber can be up to 1500 m long. The display on the front panel is a Varitronix MGLS 12864T.

The PULPO 2 Peripheral Board (see Fig. 3) contains all interfaces to the cryostat and the shutter. The core component here is a PLD that controls all the interfaces on the board and handles the communication to the CPU board.

The sensor interface contains a multiplexer group with 32 inputs. One channel is used for monitoring the vacuum in the cryostat (Balzers or Edwards gauges, set by software), another for the onboard sensing of the heater current and another for an internal calibration resistor. The other 29 channels can be used to connect external PT100 sensors (4-wire system).

The output of the multiplexers travels via a two-stage amplifier with programmable gain into a 16-bit ADC. Low gain (G=8) is used for heater current and vacuum sensing. High gain (G=72) is used for PT100 input.

Figure 3. PULPO 2 peripheral board.

PULPO 2 uses PWM (Pulse Width Modulation) for the heater control. The power dissipation inside the unit is therefore very small (~30 mO per heater). A total of 8 independent or jointly used heaters are available. The heaters are operated with the linear +24V supply in order to avoid switching noise (from the DC/DC converters) in the focal plane. The maximum heater current is 3A, giving a maximum heating power of up to 72W.

PULPO 2 also features a set of alarm outputs for temperature and vacuum. Four independent alarm outputs are available (2 for temperature and 2 for vacuum problems). The alarm values for temperature and vacuum can be configured by software and can be connected to a Central Alarm System and/or a dialer.

Optical detectors normally require a mechanical shutter to control a shutter. PULPO 2 offers 1 output (open command) and 4 inputs (open status, close status, remote, and fail). All of them are optically isolated in order to avoid ground loops. Exposure time counting and the measurement of the open and close delays are handled by the PLD. The logic for the I/O lines is programmable via the software, enabling PULPO 2 to interface with almost any type of shutter.

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