FAQ: Barometer (-IB sensor)

FAQ: How adding an internal barometer (-IB sensor) affects an Alicat device

Alicat mass flow and absolute pressure devices can be equipped with a barometer (-IB sensor) that provides barometric and gauge pressure information.  Please contact us at 888-290-6060 or info@alicat.com with any questions.

What devices can have a barometer added?

Note: Portable versions come with a barometer by default.

What are the primary features of an –IB unit?

  • Measures barometric pressure.
  • Calculates gauge pressure using readings from barometric pressure and absolute pressure sensors.
  • Controllers can control gauge pressure instead of flow rate.

Does adding an -IB sensor affect accuracy of my device?

No, the accuracy of the device will not be affected.

However, the uncertainty of the gauge pressure reading will be affected, as it is the sum of the barometer and absolute pressure uncertainties.

How do I use my -IB sensor to calibrate my absolute pressure sensor?

When the device is open to atmosphere, tare the pressure either with the front panel or over serial communication.

Can I look at both absolute pressure and gauge pressure on a device that has an -IB sensor?

Yes.  On the display, either can be selected.  By default, only the absolute pressure will be shown in the serial data frame, but this can be replaced with gauge pressure (“GP” adder code) or barometric pressure (“BP” adder code).  It’s also possible to have absolute pressure, gauge pressure, and barometric pressure all show in the data frame (“AGB” adder code).

What is the full scale range of absolute pressure for an -IB unit?

  • For standard or anti-corrosive units: 11.5 to 160 PSIA
  • For whisper units: 11.5 to 60 PSIA
  • For high pressure units:  11.5 to 320 PSIA

What is the full scale range of gauge pressure for an -IB unit?

  • For standard or anti-corrosive units: 0 to 160 PSIG
  • For whisper units: 0 to 60 PSIG.
  • For high pressure units: 0 to 320 PSIG

Note:  Bidirectional flow devices will also have bidirectional gauge pressure ranges. For example, an MCD-Series unit will have a range of -160 PSIG to +160 PSIG.

What control loops are added on an -IB unit?

Closed-loop pressure control on gauge pressure (“CLPG” adder code).

Is barometric pressure on my RS232 data frame?  Gauge pressure?  Absolute pressure?

Absolute pressure is on the RS232 data frame by default. This can be substituted with gauge or barometric pressure, or they can be added separately.

Do I have an analog output of absolute pressure, gauge pressure, or barometric pressure?

Most electrical connectors allow for two analog outputs.

  1. For a primary analog output, you can order:
    1. Absolute pressure: 5P, 10P, 1P, or CP
    2. Gauge pressure : 5PG, 10PG, 1PG, or CPG
    3. Barometric pressure : 5PB, 10PB, 1PB, or CPB
  1. For a secondary analog output, you can order:
    1. Absolute pressure: 52P, 102P, 12P, or C2P
    2. Gauge pressure : 52PG, 102PG, 12PG, or C2PG
    3. Barometric pressure : 52PB, 102PB, 12PB, or C2PB

What engineering units are the pressure readings given in?

  • Barometric pressure and absolute pressure are given in absolute pressure units.
  • Gauge pressure is given in gauge pressure units.

How do I change between barometric, absolute, and gauge pressure?

All three can be set separately via the front screen.

Do I need to order custom pressure ranges when I order an -IB unit?

No.  Since the pressure accuracy is dependent on reading, a smaller range will not make the pressure reading more accurate.  If you need a higher range than the default offers, please contact an applications engineer.

What is the barometric pressure accuracy?

±0.00725 PSI

What is the gauge pressure accuracy? Absolute pressure?

  • The gauge pressure accuracy is the uncertainty of the absolute pressure reading plus an additional 0.00725 PSI.
  • The absolute pressure accuracy can be found in the corresponding specification sheet.

I ordered an –IB unit but forgot to order it in closed-loop pressure mode.  What do I do?

The control loop variable can easily be changed via the front screen.

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