Slope Indicator’s manuals recommend that users lower the probe to the bottom of the borehole and wait 5 to 10 minutes before starting the survey. This “warm-up” period allows (1) the electronics of the probe to warm up and stabilize and (2) the mechanicals of the probe (wheels and housing) to match the temperature of the water in the casing. What happens if the user omits the warm-up period?
Readings taken during the first 5 or 10 minutes of the survey may contain an offset that later readings do not. When readings are processed, the offset error may look like movement at the bottom of the borehole. How severe are the errors? The offset error will be smallest when a warm probe (25 to 30°) is lowered into 12°C water, which is the typical groundwater temperature in moderate climates. In such conditions, a shorter, 3 to 5 minute warm-up period will provide good results. The offset error will be greatest when the probe is cold. For this reason, be sure to allow at least 10 minutes warmup time for cold probes. Note that the readout’s Ready signal does not monitor the warm-up period and should not be used for that purpose.