Kipp&Zonen LOGBOX SD Data Logger - Manual (Page 50)

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• Q: Can you explain something how a data logger works ?
• A: Every logger has an A/D converter with a certain resolution (number of bits) - you
see often 10, 12, 16 or 24 bits resolution
A logger also has a fixed number of analog input ranges - you see often 20 mV, 100
mV, 1 V, 5 V and 10 Volt ranges
Let’s take for example we use a logger with 12 bits resolution and 5 Volt input
range.
This means that the 5 Volt is divided in 2¹² steps. This is 5/4096 = 0.00122 Volt per
step
So the smallest detectable change on the input is 1.22 mV
If we connect an SP Lite with a sensitivity of 75 μVolt/W/m²
One Watt (change) will give 0.075 mV (change) on the output.
So we need a change of 1.22 / 0.075 = 16.2 Watt/m² before we see a change in the
Logger output.
As you can understand this is not acceptable
A minimum of 1 W/m² should be detected (preferably a factor 10 times better)
This can be achieved in lowering the input range to 100 mV (50 times better)
Or selecting a higher resolution e.g. 16 bits (instead of 12 bits) this is 16 times
better. ( 2¹⁶- 2¹² = 2⁴ = 16 )
• Q: What is the difference between single ended and differential?
• A: With differential inputs, two signal wires run from each signal source to the Data
logger. One goes to a + input and one to a - input. Two high-impedance amplifiers
monitor the voltage between the input and the interface ground. The outputs of the
two amplifiers are then subtracted by a third amplifier to give the difference between
the + and - inputs, meaning that any voltage common to both wires is removed.
By selecting a differential method automatically the first two inputs AIN 1 and AIN 2
for example will be the + and – input.
With single-ended inputs you connect one wire from each signal source to the data
acquisition interface. The measurement is the difference between the signal and the
ground or earth at the data logger. (which will be AIN 6 on the Logbox SD)
How to connect CNR 1 or CNR 4 to the Logbox SD
•
A: All connected as single ended and only in combination with a 10K thermistor.