The roots meter is similar in many respects to the oval gear meter. A design is shown where two-lobed impellers rotate in opposite directions to each other within the body housing. These peanut-shaped gears sweep out an exact volume of liquid passing through the measurement chamber during each rotation. The flow rate can be calculated by measuring the rotation speed. In contrast to nutating disc meters, the calibration factor does not vary with viscosity. Maximum viscosity allowed: 5,000 centipoise.

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