Campbell CR3000 Micrologger, Operator'S Manual

Page: 407 / 644

Section 8. Operation
407
Pulse Measurements: Terminals and Programming
Measurement
P
Terminals
C
Terminals
CRBasic
Instruction
Time from edge on port 1

TimerIO()
Count of edges

TimerIO()
Pulse count, period

TimerIO()
Pulse count, frequency

TimerIO()
8.1.3.1 Pulse Measurement Terminals
P Terminals
•
Input
voltage range =
–20 to 20 V
If pulse input voltages exceed
±
20 V, third-party external-signal conditioners
should be employed. Under no circumstances should voltages greater than 50 V
be measured.
C Terminals
• Input voltage range =
–8 to 16 Vdc
C terminals configured for pulse input have a small 25 ns input RC-filter time
constant between the terminal block and the CMOS input buffer, which allows for
high-frequency pulse measurements up to 250 kHz and edge counting up to 400
kHz. The CMOS input buffer recog
nizes inputs ≥3.8 V as being high and inputs
≤1.2 V as being low.
Open-collector (bipolar transistors) or open-drain (MOSFET) sensors are
typically measured as frequency sensors. C terminals can be conditioned for open
collector or open drain with an external pull-up resistor as shown in figure
Connecting Switch Closures to C Terminals Configured for Control. The pull-up
resistor counteracts an internal 100 kΩ pull
-down resistor, allowing inputs to be
pulled to >3.8 V for reliable measurements.
8.1.3.2 Low-Level Ac Measurements — Details
Related Topics:
• Low-Level Ac Input Modules — Overview
(p. 431)
• Low-Level Ac Measurements — Details
(p. 407)
• Pulse Input Modules — List
(p. 604)
Low-level ac (sine-wave) signals can be measured on P terminals. Sensors that
commonly output low-level ac include:
•
Ac generator anemometers