Campbell-scientific CR3000 Micrologger Instrukcja Użytkownika Pobierz pdf (Strona 321)

Section 8. Operation

321

8.1.5.1.2 Low-Level ac (P1 - P4)

Rotating magnetic-pickup sensors commonly generate ac output voltages ranging

from thousandths of Volts at low rotational speeds to several volts at high

rotational speeds. Pulse channels contain internal signal-conditioning hardware

for measuring low-level ac-output sensors. When configured for low-level ac, P1

through P4 measure signals ranging from 20-mV RMS (±28 mV peak) to 14-V

RMS (±20 V peak). Internal ac coupling is incorporated in the low-level ac

hardware to eliminate dc offset voltages of up to ±0.5 Vdc.

8.1.5.1.3 Switch Closure (P1 - P4)

Switch-closure mode measures switch closure events, such as occur with a

common tipping bucket rain gage. An internal 100-kΩ pull-up resistor pulls an

input to 5 Vdc with the switch open, whereas a switch closure to ground pulls the

input to 0 V. An internal 3.3-ms time-constant RC-debounce filter eliminates

multiple counts from a single switch closure event.

8.1.5.2 Pulse Input on Digital I/O Channels C1 - C8

Digital I/O channels C1 – C8 can be used to measure pulse inputs between -8.0

and +16 Vdc. Low frequency mode (<1 kHz) allows for edge timing and

measurement of period and frequency. High-frequency mode (up to 400 kHz)

allows for edge counting only. Switch-closure mode enables measurement of dry-

contact switch closures up to 150 Hz. Digital I/O channels can be programmed

with either PulseCount() or TimerIO() instructions.

When configured for input, signals connected to C1 – C8 are each directed into a

digital-CMOS input buffer that recognizes inputs  3.8 V as being high and inputs

 1.2 V as being low.

Low-level ac signals cannot be measured directly by digital I/O channels. Refer

to the appendix Pulse / Frequency Input-Expansion Modules

(p. 562) for information

on peripheral modules available to convert low-level ac signals to square-wave

signals.

Read More! Review digital I/O channel specifications in CR3000 Specifications



Caution Contact Campbell Scientific for signal conditioning information if a

pulse input < -8.0 or > +16 Vdc is to be measured. Under no circumstances

should voltages greater than ±50 V be connected to channels C1 – C8.

8.1.5.2.1 High Frequency Mode

Digital I/O channels have a small 25-ns input RC-filter time constant between the

terminal block and the CMOS input buffer, which allows for higher-frequency

pulse counting (up to 400 kHz) when compared with pulse-input channels P1 –

P4 (250 kHz maximum).

Switch-closure mode is a special case edge-count function. Because of signal

conditioning for debounce, 150 Hz is the maximum input frequency at which

switch closures can be measured on digital I/O channels.

1 2 ... 316 317 318 319 320 321 322 323 324 325 326 ... 589 590

Komentarze do niniejszej Instrukcji

Brak uwag

Campbell-scientific CR3000 Micrologger Instrukcja Użytkownika Strona 321

Komentarze do niniejszej Instrukcji

Powiązane produkty i podręczniki dla Urządzenia pomiarowe Campbell-scientific CR3000 Micrologger