Digital Control Circuit; Temperature Circuits; Programmable Gain Amplifier Circuitry - Bayer HealthCare RapidPoint 400 Series Service Manual

Digital Control Circuit

R27 and C54, along with three of the inverters from U14, form an oscillator
(approximate frequency of 20 kHz) that drives a state machine formed by
U15, U21, U22, and U27. This state machine produces all of the signals
necessary to operate the amperometric and hematocrit circuits.

Temperature Circuits

A thermistor that is connected thermally to the sample path senses the
sample temperature. This resistance is converted into a voltage measured
by the DAS circuitry on the Main board.
Additionally, it is necessary to monitor the temperature of the connector
block and the sample preheater. This monitoring is accomplished with two
29.07K ohms thermistors: the block and the preheater thermistors.

Programmable Gain Amplifier Circuitry

To optimize the dynamic range offered by the ±5 V A/D converter on the
Main board, it is necessary to adjust the offset voltage and set the gain of
each signal before it is cabled down to the Main board.
U20 buffers the DAC_PGA offsetting signal and drives the bottom of the
gain resisting network for U17.
106 Rev. C