Campbell Scientific LLAC4 Four-channel, Low-Level AC Conversion Module - Manual (Page 8)

LLAC4 Four-Channel, Low-Level AC Conversion Module
2. Specifications
Power: 8 to 16 Vdc
0.1 mA @ 12 Vdc
Signal Conditioning: Minimum AC Input Voltage versus
Output Square Wave Frequency:
Input Sine Wave
(mV RMS)
20
200
2000
5000 Output Square
Wave Range (Hz)
1.0 to 20
0.5 to 200
0.3 to 10,000
0.3 to 20,000
AC Coupling Removes DC Offset: up to ±0.5V
Input Hysteresis: 16 mV @ 1 Hz
Max AC Input Voltage: ±20 V
Dimensions: 8.0 W x 5.4 H x 2.5 D cm
(3.1 in x 2.1 in x 1.0 in)
11.2 W x 5.4 H x 2.5 D cm
(4.5 in x 2.1 in x 1.0 in)
including base mounting flange
Cable Length 0.6 m (2 ft)
Weight: 92 g (3.2 oz)
3. Measurements
Sensors, such as anemometers, may produce a sinusoidal AC signal output
where the frequency is proportional to the speed of rotation. This AC signal is
induced in a stationary coil by a magnet mounted on a rotating shaft.
The datalogger’s pulse channels can read this low-level AC signal directly.
The LLAC4 has signal conditioning to convert the low-level AC to a 0 to 5
volt square wave that can be measured on the datalogger’s control ports. The
frequency response of the LLAC4 is the same as the low-level AC on the pulse
inputs.
Typically, propeller type anemometers operate at higher frequencies than cup
anemometers at the same wind speed (see Table 1).
TABLE 1. Sensor Output Frequencies
Sensor Output @ 50m/s Type
05103 510Hz Propeller
03101 67Hz Cup
The datalogger must also be able to read these high frequency pulses on its
control ports. Table 2 shows some common dataloggers and their compatible
control port specifications.
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