For example, in a 1000 mm level measurement, 250 mm of material covering the sensor represents an equivalent capacitance level measurement of 250 mm. For an accuracy of 1 percent of measured distance, the absolute error can be calculated as:

Level Probe Coverage Absolute Error

0% (MT) 0 mm 1% of 0 = 0.0 mm

25% 250 mm 1% of 0 = 2.5 mm

50% 500 mm 1% of 0 = 5.0 mm

75% 750 mm 1% of 0 = 7.5 mm

100% 1000 mm 1% of 0 = 10.0 mm

However, a radar level measurement system with 250 mm of material covering the sensor would measure 750 mm from the top of the sensor to the material. For an accuracy of 1 percent of measured distance using a radar level measurement system, the absolute error can be calculated as:

Level Probe Coverage Absolute Error

0% (MT) 0 mm 1% of 1000 = 10.0 mm

25% 250 mm 1% of 750 = 7.5 mm

50% 500 mm 1% of 500 = 5.0 mm

75% 750 mm 1% of 250 = 2.5 mm

100% 1000 mm 1% of 0 = 0.0 mm

A *percentage of set span* statement describes a parameter that can be in error by a constant percentage of the set span of the transmitter. In a measurement using a transmitter measuring a 1000 mm level with an accuracy of 1 percent of set span, the absolute error can be calculated as:

Level Probe Coverage Absolute Error

0% (MT) 0 mm 1% of 1000 = 10.0 mm

25% 250 mm 1% of 1000 = 10.0 mm

50% 500 mm 1% of 1000 = 10.0 mm

75% 750 mm 1% of 1000 = 10.0 mm

100% 1000 mm 1% of 1000 = 10.0 mm

Excerpted from The Consumer Guide to Capacitance and Radar Level Gauges