Campbell CR3000 Micrologger, Руководство оператора

Страница: 409 / 644

Section 8. Operation
409
P Terminals
• Maximum input frequency = 250 kHz
•
CRBasic instructions: PulseCount()
High-frequency pulse inputs are routed to an inverting CMOS input buffer with
input hysteresis. The CMOS input buffer is at output 0 level with inputs
≥
2.2 V
and at output 1 level with inputs
≤
0.9 V. An internal 100 k
Ω
resistor is
automatically connected to the terminal to pull it up to 5 Vdc. This pull-up resistor
accommodates open-collector (open-drain) output devices.
C Terminals
•
Maximum
input frequency = <1 kHz
•
CRBasic instructions: PulseCount(), TimerIO()
8.1.3.3.1 Frequency Resolution
Resolution of a frequency measurement made with the PulseCount() instruction
is calculated as
where
FR = r
esolution of the frequency measurement (Hz)
S = scan interval of CRBasic program
Resolution of a frequency measurement made with theTimerIO() instruction is
where
FR = frequency resolution of the measurement (Hz)
R = timing resolution of the
TimerIO()
measurement = 136 ns
P = period of input signal (seconds). For example, P = 1 / 1000 Hz = 0.001
s
E = Number of rising edges per scan or 1, whichever is greater.
Example: E for a 10 Hz input signal
Scan Rising Edge / Scan E
5.0 50 50
0.5 5 5
0.05 0.5 1