Why does the instrument have multiple ranges?
At very low concentrations of mercury vapor (below about 20 micrograms per cubic meter) it takes a long time to collect enough mercury on the sensor to get an accurate reading. For this reason, a range that samples for 30 seconds is provided. At action levels (for example 50 micrograms per cubic meter) a sufficient sample is obtained in seven seconds. This is the normal or default operating range. At higher (dangerous) levels so much mercury adsorbs on the sensor that the sensor capacity is used up in a few samples so a shorter sampling time of two seconds is used. At saturation levels (10 to 20 milligrams per cubic meter) an even shorter sample of ½ second is used. The instrument prompts the operator to change ranges as appropriate.
