User`s manual

PK2100
I/O Configurations s 3-9
g = 10 =
R5 + RP5A
R5
×
RP5B
RP5B
+ R11
Jumper H7 installed
The gain at the plus and minus inputs is 10 when jumper H7 is installed.
The gain of the plus input becomes higher (11) when H7 is removed. This
has the effect of skewing the output from a nulled bridge circuit to the
middle of the measurement range. Such a bridge circuit is shown in
Figure 3-9 below. When the bridge is nulled, both inputs are equal to 5
volts. The output voltage of the input amplifier with H7 removed is 5 ×
(11 - 10) = 5volts. This is in the middle of the 10-volt measurement
range of
to High-sensitivity
differential input
+10-V reference
Variable element
(thermistor,
RTD, etc.)
Figure 3-9. Nulled Bridge Circuit for Measuring
High-Sensitivity Differential Analog Input
010volts.
The bridge makes it possible to detect changes of ±0.04 percent in the
value of the variable-resistor element when the gain is 10. A change of
only ±0.2 percent can be detected without a bridge.
The gain for the negative input, AD, is given by RP5A/R5. The gain for
g = 11 =
R5 + RP5A
R5
× (1). Jumper H7 not installed
the positive input, AD+, is given by:
or
The calibration gain and offsets are stored in the EEPROM (see
AppendixE).
The output voltage, y, is given by
y = a
1
× (x
1
+ a
0
) - b
1
× x
2
where
x
1
and x
2
are the positive and negative inputs, respectively,
a
1
is the positive-side gain,
a
0
is the positive-side offset, and
b
1
is the negative-side gain.
Note that b
1
is also equal to the calibrated value of a
1
(with Jumper H7 not
connected) minus 1, that is, b
1
= a
1
- 1.