How does a data logger work?
Every logger has an A/D converter with a certain resolution (number of bits) – often 10, 12, 16 or 24 bits resolution. A logger also has a fixed number of analog input ranges – often 20 mV, 100 mV, 1 V, 5 V and 10 Volt ranges. 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(2) with a sensitivity of 75 microVolt/W/m^2, 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 by lowering the input range to 100 mV (50 times better). Or by selecting a higher resolution e.g. 16 bits (in stead of 12 bits) this is 16 times better ( 2¹⁶- 2¹² = 2⁴ = 16 )
