Specifications

Section 4. Sensor Support
4-2
4.1.3 Continuous Unregulated (Nominal 12 Volt)
Voltage on the 12 V terminals will change with CR1000 supply voltage.
4.1.4 Switched Unregulated (Nominal 12 Volt)
Voltage on the SW-12 terminal will change with CR1000 supply voltage. Two
CRBASIC instructions, SW12() and PortSet(), control the SW-12 terminal.
Each is handled differently by the CR1000.
SW12() is a processing task instruction. Use it when controlling power to
SDI-12 and serial sensors, which use SDI12Recorder() or SerialIn()
instructions respectively. CRBASIC programming using IF THEN constructs
to control SW-12, such as cell phone control, should also use the SW12()
instruction.
PortSet() is a measurement task instruction. Use it when powering analog
input sensors that need to be turned on just prior to measurement.
TABLE 4.1-1. Current Sourcing Limits
Terminals
Vx/EX1, Vx/EX2, Vx/EX3
Current Source Limit
±25 mA Maximum
SW12 < 900 mA @ 20°C
< 730 mA @ 40°C
< 650 mA @ 50°C
< 570 mA @ 60°C
< 360 mA @ 85°C
12V + SW12 < 3.00 A @ 20°C
< 2.49 A @ 40°C
< 2.31 A @ 50°C
< 2.04 A @ 60°C
< 1.56 A @ 85°C
5V + CSI/O < 200 mA
4.2 Voltage Measurement
The CR1000 measures single-ended (SE) and / or differential (Diff) voltage
inputs. Single-ended measurements use CRBASIC instruction VoltSE(), which
returns the voltage difference between a single input (x.x mV) and ground (0
mV). Differential measurements use CRBASIC instruction VoltDiff(), which
returns the voltage difference (x.x - y.y) between a high input (x.x mV) and a
low input (y.y mV).
Associated with differential measurements is common-mode voltage, defined
as the average DC voltage common to both the high and low inputs [(VHi +
VLo) / 2] associated with a differential measurement. The CR1000
incorporates a differential instrumentation amplifier on its measurement front-
end. This amplifier processes the difference between the voltage inputs, while
rejecting common-mode signals, as long as the common-mode signals are