User`s manual
PK2100
I/O Configurations s 3-5
software (see Chapter 4, System Development) provides the two thresh-
olds.
The universal inputs are protected against overloads between -48 and
+48volts. The analog resolution is 10 bits, providing approximately 1024
steps over the range 010 volts (07volts for PK2110/PK2130). Its
sensitivity is about 10 millivolts per step.
Figure 3-3 shows a schematic of a single universal input channel.
Each input uses a comparator driven by the signal and by an internal DAC
to measure the input voltage. The input resistor and capacitor filter out
high-frequency noise and provide protection against overloads. Clamp
diodes in the LM339A provide additional protection against overload.
The input has a high D.C. impedance unless one of the jumpers is con-
nected. If the excitation resistor is connected, the circuit provides an
excitation voltage or current to an external device. This is convenient for
measuring an external resistance such as a potentiometer or a temperature
sensor (Figure 3-4).
+3.3-kΩ excitation
+resistor
430-Ω resistor, 420 mA loop,
channel 6 only. Connect H5:78
0.01 µF
UEXP
value or fixed reference (
RR
)
+
comparator
LM339A
Jumpers
(H4, H5, H6)
Input
VCC
10 kΩ
22 kΩ
4.7 kΩ
+10-V reference
Figure 3-3. Universal Input Channel
3.3 kΩ
8 kΩ
+10-V reference
Temperature Sensor
3.3 kΩ
+10-V reference
Figure 3-4. Measuring Variable External Resistance