iSource
®
StarLPRO-1500
Manual
©SpectraTime
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Page 11 of 12
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4.4
PIN FUNCTION LAYOUT
The following table is providing the pin function description of the StarLPRO-1500 along with comparison with
the LPRO from other vendor.
4.5
NORMAL OPERATION
When 12 Vdc (or 24V) is applied to pins 10 (+) and 4, 8 (-), the unit will immediately begin to generate a 10 MHz
signal from the crystal oscillator. Within approximately 12 minutes (standard version) after application of input
power the unit will "lock". Hence the crystal is now stabilised by the atomic resonant frequency.
The unit is able to provide a single signal called ‘lock monitor’ (pin 6) which toggles to high level when the
internal crystal oscillator is locked to the Rb atomic resonance. (see chapter 4.7).).
4.5.1 ANALOG FREQUENCY ADJUSTMENT
The STARLPRO-1500 is equipped with an analog frequency adjustment circuit which provides center frequency
adjustment by applying an external voltage of 0 to 5V on Pin 7. Center frequency adjusted at factory is made by
leaving this pin open using internal voltage reference of 2.5V +-5%. This means, applying 2.5V on this pin may
induce a small frequency offset related to factory setting. To avoid such frequency offset, it is recommended to
measure the voltage on the pin 7 first and then apply the same voltage value on the pin 7 to recover the exact
voltage as applied for the factory setting. Furthermore, the StarLPRO offers adjustment capabilities using
internal potentiometer adjustable with a small screwdriver to right side of connector (see drawing 4-4).
4.6
SERIAL INTERFACE OPERATION
4.6.1 INTRODUCTION
The STARLPRO-1500 is equipped with a microcomputer, associated with multi-channel D/A converters, used
for setting its parameters. This microcomputer is also used for the interrogation and detection of the Rb
absorp
tion ‘ dip’.
The built-in serial interface allows an automatic parameter adjustment during the manufacturing process as well
as coarse and fine adjustment of the centre frequency.
All the working parameters are stored in a built-in EEPROM memory. In addition an 8 channel A/D converter is
used for monitoring the main internal signals such as: light level, signal level, thermostats heating currents etc...
