Video: Understanding how to tare your Alicat device

Understanding how to tare your Alicat device

What is tare? Why is it important? And how do I tare?

Setting the tare takes a sensor signal and sets it as zero in flow or pressure. A zero setpoint results in closing of the valve (on controllers, not meters) and creates a known “no flow” condition. Tare makes readings more accurate by removing cumulative errors from drift.

An analogy might be a bathroom scale. By getting on and then off a bathroom scale repeatedly over time, the needle may no longer return to pointing at zero. On mechanical scales, one could see this: with no weight on the scale, the pointer might point to more or less than zero. If it pointed to +1, and you weighed yourself, the reported number would be your actual weight, plus one—the scale would read your weight as heavier than it should (which is always unacceptable!) These scales had a small knob or dial, usually on the front or back bottom edge, to adjust the dial reading back to zero. But you would need to adjust the pointer only when there was no weight on the scale, or else you introduced an error.

Similarly, many measurement devices need to have tare set to remove this drift periodically. Improperly setting tare (when flow is occurring) of an Alicat instrument will result in inaccurate readings as well, since the flow that was occurring during the tare will be subtracted from the true reading.

This video shows how to set a tare manually using the display buttons, and how to turn on or off the Auto-Tare function, which tares the flow controller automatically whenever a 0 setpoint occurs.

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