Metal Samples MS2500L, Руководство оператора

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D. Circuit Description
The following circuit description describes the behavior of the circuitry in the LPR mode with the output
mode set to SAMPLE. This is the most common mode of operation for this type of instrument. Differ-
ences in operation modes are described in following sections.
Power Supplies
The power supply circuitry is contained on the A2 Board. This includes:
• A 2.5 volt reference circuit made up of U9 and CR6.
• The main 6 volt source maintained by AR5-A and Q2.
• The 1 volt common reference maintained by AR6.
• The Auxiliary common reference and supply consisting of AR5-A and AR5-D.
The constant current IC, U9, and the micropower reference diode, CR6, maintain a stable 2.5 volt
reference. This reference is amplified and regulated at 6 volts by AR5-A. Since this is the main power
source for the circuitry, the 2N2222 transistor, Q2, in the feedback loop of AR5-A adds extra current
drive. AR6 contains a built-in 200 millivolt reference and a power OP-amp. Together these are used to
supply a 1 volt common source for most of the analog and digital circuitry. AR5-C and AR5-D are unity
gain buffers used to supply the power to the clock circuitry which tend to degrade the power supplies.
Clock, Timer and Power On Reset Circuit
The clock, timing and power on reset circuitry are contained on the A2 Board. These circuits consist of:
• A power on reset pulse generator; U17.
• A clock oscillator and divider circuit consisting of U16 and U12.
• A user programmable timer circuit made up of U8, U10, and U11, and SW3, SW4, and SW5.
Upon power up, a pulse is generated by U17 which sets the initial states of the timer circuits to the user
selected BCD value using SW3, SW4, and SW5. The timers are cascaded in order to count down
upon every pulse generated from the Q14 output of U12. Upon each completion of