A voltage divider will drop the voltage of the input signal to the level the data logger can measure. Onset offers several adapter cables that include voltage divders, specifically:
This instruction will help you create your own voltage divider if you so desire.
First determine the needed attenuation ratio; divide the input volts by the output volts to the data logger: A = input volts/2.5.
If the maximum signal is 5 volts DC, and you wish to use the HOBO's full-scale range of 2.5 volts DC, the attenuation is 2:1, or just 2.
Once you have determined the attenuation (A), you can calculate for the Resistor (R1). For now, pick a value for R2 (typically 10k), then calculate for R1.
R1 = (A - 1) *R2
From the above example A = 2 and, if you picked a value of 10,000 for
R2: R1 = (2 - 1) *10,000
R1 = 10,000 ohms
Therefore, R1 and R2 are both 10K resistors.
There are a few practical considerations. If the sum of R1 and R2 is too low (Rmin), you could overload your input source or heat up the resistors. If the sum of R1 and R2 is too high (Rmax), it could be a poor match for our volt data logger's 10K input impedence. Also, resistors do not come in every possible resistance value. You will have to plug in available resistance values until you reach a voltage divider that is both accurate enough and keeps the sum of R1 and R2 within practical limits.