Figure 4-1 Signal Phase
In the signal phase (see Figure 4-1), the source voltage V
S
is connected to the sen-
sor R
T
. The current that flows through R
T
also flows into the collector of Q101. The
output voltage of U104C is charged on capacitor C106. Also during this phase, the
input to U104A is grounded and the voltage developed is charged on capacitor
C105.
In the zero phase, the two charged values of voltage are transferred to other parts
of the circuit, as depicted by Figure 4-2. The source voltage V
S
is disconnected
from the sensor and connected to a zero reference resistor R
Z
. The current that
flows through R
Z
also flows in the collector of Q101. The output voltage of U104C
is connected REF LO on U102 by way of C106 and U103B (see Schematic
Diagram 866-106 or 865-106). The voltage that is applied to the input of U104A
and across C111 is the difference between the output voltage of U104C and the
voltage that was charged on C106 during the signal phase.
The voltage charged on C105 is now opposing the output of U104A and therefore
transferred to C110. This is the voltage digitized by the A/D converter (U102). The
fixed reference HI voltage for U102 is provided by current source U105 and its
associated resistors.
5
Summary of Contents for 865
Page 1: ...http www omega com e mail info omega com User sGuide Model 865 and 866 Digital Thermometers ...
Page 22: ......
Page 23: ......
