DigiVac Bullseye Precision Gauge Piezo Manuel de l'utilisateur - Page 13

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matter or water from entering the display and controller electronics. The unit is not water

proof, so splashes of water while the gauge is powered on can damage the electronics. If a

weather proof version is required, consult DigiVac.

There is inherent drift in all sensors including the DigiVac 775i piezo resistive sensor. Drift is

specified in the datasheet, but the specification is typically a worst case scenario as drift is not

easily predicted and depends on operating environment. Depending on your accuracy

requirements, it makes sense to set up a calibration interval to obtain as found data, and get a

fresh calibration. Having this information will allow you to determine the optimal calibration

interval. The accepted interval is 1 year, but depends on what accuracy you require and what

you've defined in your standard operating procedures.

Note the sensors have excellent accuracy by themselves. Additional accuracy is gained by

calibrating the sensor controller (the thing with the display and cable coming out of it) to the

sensor. The sensor itself is cannot be calibrated, but the sensor-controller pair is. See our

blog on sensor interchangeability effects on accuracy for the Bullseye Precision Gauge Piezo

for more information.

Note that the 775i sensors accuracy applies to any type of measurable gases. Readings will be

correct regardless of the type of gas you are trying to measure.

Vacuum Calibration

The calibration screen contains the numbers necessary to calibrate the gauge to a known

good standard. The "Vacuum" number on in the top right corner is millitorr x 10. For

example, in the above picture 3.1 millitorr is displayed. The next number is counts, which is an

internal number that literally represents what is coming into the microcontroller's A2D

converter, and is a useful diagnostic. The numbers on the bottom are:

• AT – the Atmospheric pressure calibration number

• MID – The middle calibration number. This number literally represents the calibration

curve pivot point between the AT and VAC variables

• VAC – the vacuum or low pressure calibration number

These numbers on the bottom represent the digital calibration points to be adjusted in order

to achieve optimal calibration. There are 2 ways to calibrate: Manually and Automatically.