Internal barometer (-IB sensor) FAQ

• Alicat’s differential pressure based mass flow meters and controllers.
• Alicat’s absolute pressure gauges, controllers, and dual-valve controllers.

Note: All portable devices come with a barometer by default.

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

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.

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

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 is also possible to have absolute pressure, gauge pressure, and barometric pressure all show in the data frame (“AGB” adder code).

• 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

• 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.

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

Absolute pressure is on the RS-232 data frame by default. This can be substituted with gauge or barometric pressure, or they can be added separately.

Most electrical connectors allow for two analog outputs.

1. For a primary analog output, you can output:
   1. Absolute pressure: 5P, 10P, 1P, or CP
   2. Gauge pressure : 5PG, 10PG, 1PG, or CPG
   3. Barometric pressure : 5PB, 10PB, 1PB, or CPB

2. For a secondary analog output, you can output:
3. 1. Absolute pressure: 52P, 102P, 12P, or C2P
   2. Gauge pressure : 52PG, 102PG, 12PG, or C2PG
   3. Barometric pressure : 52PB, 102PB, 12PB, or C2PB

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

All three can beset separately using the front stand-up interface.

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.

±0.00725 PSI

• 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 appropriate specification sheet.

The control loop variable can easily be changed using the front stand-up interface.