Campbell Scientific CR1000KD CR1000 Measurement and Control System - Page 315

High-frequency Pulse P1 - P2, 1.5.1.2 Low-Level ac P1 - P2, 1.5.1.3 Switch Closure P1 - P2

Page 315 highlights

Section 8. Operation 8.1.5.1.1 High-frequency Pulse (P1 - P2) High-frequency pulse inputs are routed to an inverting CMOS input buffer with input hysteresis. The CMOS input buffer is an output zero level with its input ≥ 2.2 V, and an output one level with its input ≤ 0.9 V. When a pulse channel is configured for high-frequency pulse, an internal 100-kΩ pull-up resistor to 5 Vdc on the P1 or P2 input is automatically employed. This pull-up resistor accommodates open-collector (open-drain) output devices for high-frequency input. 8.1.5.1.2 Low-Level ac (P1 - P2) 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 P2 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 - P2) 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 ( +16 Vdc is to be measured. Under no circumstances should voltages greater than ±50 V be connected to channels C1 - C8. 315

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Section 8.
Operation
315
8.1.5.1.1 High-frequency Pulse (P1 - P2)
High-frequency pulse inputs are routed to an inverting CMOS input buffer with
input hysteresis. The CMOS input buffer is an output zero level with its input
2.2 V, and an output one level with its input
0.9 V.
When a pulse channel is
configured for high-frequency pulse, an internal 100-k
Ω
pull-up resistor to 5 Vdc
on the
P1
or
P2
input is automatically employed. This pull-up resistor
accommodates open-collector (open-drain) output devices for high-frequency
input.
8.1.5.1.2 Low-Level ac (P1 - P2)
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
P2
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 - P2)
Switch-closure mode measures switch closure events, such as occur with a
common tipping bucket rain gage. An internal 100-k
Ω
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. 560)
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 CR1000 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
.