Campbell Scientific CR7 Measurement and Control System - Manual (Page 27)

CR7 MEASUREMENT AND CONTROL SYSTEM OVERVIEW
OV-17
OV6. SPECIFICATIONS
Electrical specifications are valid for over a -25° to +50°C range unless otherwise specified.
Analog Inputs
(723T or 723 Card specifications below;
726 ±50 V Card specifications discussed in
System Description )
Voltage Measurement Types: Single-ended or
differential.
Range and Resolution: Ranges are software
selectable on any input channel.
Full Scale Resolution
Input Range (mV) Differential Single-ended
±5000 166 µ V 333 µ V
±1500 50 µ V 100 µ V
±500 16.6 µ V 33.3 µ V
±150 5 µ V 10 µ V
±50 1.66 µ V 3.33 µ V
±15 500 nV 1000 nV
±5 166 nV 333 nV
±1.5 50 nV 100 nV
Accuracy of Voltage Measurements:
Differential: ±0.02% FSR (±0.01%, 0-40°C)
(e.g. ±0.02% FSR = ±2.0 mV for ±5 V range)
Positive single-ended: ±0.02% FSR
(±0.01%, 0-40°C) ±5 µ V
Negative single-ended: ±0.03% FSR
(±0.015%, 0-40°C) ±5 µ V
Input Sample Rates: Fast A/D conversions are
integrated over 250 µ s. Slow A/D conversions
are integrated over 16.67 ms for 60 Hz AC
rejection or optionally, 20.0 ms for 50 Hz AC
rejection. Differential measurements include
two conversions, one with reversed input polar-
ity, to reduce thermal offset and common mode
errors. The following intervals do not include
the self-calibration measurement which occurs
once per instruction.
Input sample Typical input
rates noise
ms/channel nV/RMS
Fast Single-ended 2.9 350
Fast Differential 4.7 250
Slow Single-ended 22.0 43
Slow Differential 43.0 30
Fast Differential (TC) 7.9 250
Common Mode Range: ±5 V
Common Mode Rejection: > 140 dB (DC to 100 Hz)
Normal Mode Rejection: 70 dB (60 Hz with
slow differential measurement)
Input Current: 100 pA max
Input Current Noise: 9 pA RMS (slow differential)
Input Resistance: 2.5 G Ω typical
Sustained Input Voltage without Damage:
≤ ±16 VDC
Pulse Counters
(724 Card)
Pulse Counters per Card: 4
Maximum Counts per Interval: 32,767 (with
overrange detection)
Modes: Programmable modes are switch
closure, high frequency pulse, and low level AC.
Switch Closure Mode
Minimum Switch Closed Time: 1 ms
Minimum Switch Open Time: 4 ms
Maximum Bounce Time: 1.4 ms open without
being counted.
High Frequency Pulse Mode
Minimum Pulse Width: 2 µ s
Maximum Input Frequency: 250 kHz
Voltage Thresholds: The count is incremented
when the input voltage changes from below
1.5 V to above 3.5 V.
Maximum Input Voltage: ±20 V
Low Level AC Mode
This mode is used for counting the frequency
of low voltage, sine wave signals.
Input Hysteresis: 11 mV
Maximum AC Input Voltage (RMS): 20 V
Frequency Range:
Minimum AC Input Voltage Range (Hz)
(mV RMS)
15 1 to 100
25 1 to 1,000
50 1 to 3,000
160 1 to 10,000
Digital Control Outputs
(725 Card)
Each card includes 8 digital control outputs.
Output Voltages (no load):
High: 5.0 V ±0.1 V
Low: < 0.1 V
Output Resistance: 400 Ω
Analog Outputs
(725 Card)
Each card contains 8 switched and 2 continuous
analog outputs.
Switched: Provides a precision voltage for
resistance measurement, then switches off
(high impedance). Only one switched output
can be active at a time.
Continuous: A preset voltage is held until
updated. Voltage degrades 0.17 mV every 7
seconds. All continuous analog outputs (and
digital control ports) can be active simultane-
ously.
Range: ±5 V
Resolution: 166 µ V
Accuracy: Same as voltage measurements.
Output Current: 25 mA at ±5 V, 50 mA at ±2 V
Resistance and Conductivity
Measurements
(Combination of 723 and 725 Cards)
Accuracy: ±0.01% of full scale bridge output
provided the matching bridge resistors are not
the limiting factor.
Measurement Types: 6-wire and 4-wire full
bridge, 4-wire, 3-wire, and 2-wire half bridges.
High accuracy, low impedance bridge
measurements are made ratiometrically with
dual polarity measurements of excitation and
output to eliminate thermal emfs. AC resis-
tance and conductivity measurements use a
750
µ s excitation pulse with the signal integra-
tion occurring over the last 250 µ s. An equal
duration pulse of opposite polarity is applied
for ionic depolarization.
Transient Protection
All input and output connections to the I/O
Module are protected using spark gaps that
are rated to 10,000 A. The spark gaps are
connected directly to a heavy copper bar on
each input card with no more than 2 inches of
20 AWG copper wire.
Control Module
Processor: Hitachi 6303
Memory: 24K ROM; 40K RAM, 709 Card
provides an additional 512K RAM.
Data Storage: 18.8K values, standard; 280K
values, expanded.
Display: 8 digit LCD (0.5” digits).
Peripheral Interface: 9-pin, D-type connector
on the Control Module panel for connection to
storage module, card storage module,
multidrop interface, modem, printer, or RS-232
adapter. Baud rates selectable at 300, 1200,
9600, and 76,800.
I/O Module Interface: Optically isolated current
loops allow connection of up to 4 I/O Modules.
I/O Modules can be separated from the Control
Module by up to 1,000 feet.
Clock Accuracy: ±1 minute per month.
Maximum Program Execution Rate: System
tasks can be initiated in sync with real-time up
to 80 Hz.
System Power Requirements
Voltage: 9.6 to 15 VDC
Typical Current Drain: 3.5 - 6 mA (minimum
system) quiescent, 16 mA during processing,
100 mA during analog measurement.
Internal Batteries: Sealed rechargeable with
2.5 Ahr capacity per charge.
Charging Circuit: Requires DC or rectified AC
voltage from 15 to 25 V. Thermal compensa-
tion is included to optimize charging voltage
according to ambient temperature.
External Batteries: Any 12 V external battery
can be a primary power source; internal batter-
ies provide a backup while the external
batteries are changed.
Operation from AC Sources: An AC operated
battery charger is included with the enclosure
to maintain full charge on the batteries where
AC power is available. In the event of power
failure, the internal batteries will keep the
system operational for up to 5 days in most
applications.
Physical Specifications
Size: ENC 7L 17” x 12” x 6”
ENC 7F 20” x 13” x 10”
ENC 7XL 19” x 19” x 10”
Weight: ~40 lbs (ENC 7F with 700X, 720, &
seven I/O cards).
Warranty
Three years against defects in materials and
workmanship.