I’ve had this discussion with chat gpt and it is interesting to see how leading questions can lead to spurious answers.
What is better barg or bara for use with compressed gas filling equipment?
Barg and bara are both units of pressure measurement commonly used in the field of compressed gas filling equipment. However, which unit is better to use depends on the specific application and context. Barg (bar gauge) measures pressure relative to atmospheric pressure, while bara (bar absolute) measures pressure relative to a perfect vacuum. In other words, barg includes the atmospheric pressure as a reference point, while bara does not. If you are using compressed gas filling equipment in a location where atmospheric pressure varies significantly, such as at high altitudes or in areas with rapidly changing weather patterns, it may be more appropriate to use bara to avoid inaccuracies due to changes in atmospheric pressure. On the other hand, if atmospheric pressure is relatively stable in your location, barg may be sufficient for your needs. It’s also important to note that different types of equipment and processes may have different pressure requirements and specifications. It’s always best to consult the manufacturer’s recommendations or the relevant industry standards to determine the appropriate pressure measurement unit for your specific application.
If we are stuck with bara how do we equate that back to barg if the atmospheric conditions have changed over the course of a day?
If atmospheric conditions have changed over the course of a day, it is important to take that into account when converting between bara and barg.
To convert from bara to barg, you need to subtract the current atmospheric pressure from the bara reading. If the atmospheric pressure has changed since the initial measurement was taken, you will need to use the current atmospheric pressure in your calculation.
One way to obtain the current atmospheric pressure is to use a barometer or to check the local weather forecast, as they typically report the atmospheric pressure. Once you have the current atmospheric pressure, you can subtract that value from the bara reading to obtain the corresponding barg value.
For example, if the initial measurement was taken at a time when the atmospheric pressure was 1013 mbar and the reading was 2 bara, and the current atmospheric pressure is now 1008 mbar, the corresponding barg reading would be:
2 bara – (1013 mbar – 1008 mbar) = 1.995 barg
It’s important to note that atmospheric pressure can fluctuate significantly throughout the day, so it’s best to use the most up-to-date and accurate atmospheric pressure measurement available at the time of conversion.
I do believe your equation is incorrect. If the initial measurement was 2.000 bara, made on a day when atmospheric pressure was 1013 mbar, and atmospheric pressure is now 1008 mbar then the current pressure in barg is = 2.000 – 1.008 which is 0.992 barg
Apologies for the confusion in my previous response. You are correct, and I apologize for the incorrect equation. The correct calculation to convert from bara to barg when the atmospheric pressure has changed is to subtract the current atmospheric pressure from the bara reading.
Using your example:
Initial measurement: 2.000 bara
Initial atmospheric pressure: 1013 mbar
Current atmospheric pressure: 1008 mbar
To convert from bara to barg, you would subtract the current atmospheric pressure from the bara reading:
2.000 bara – (1008 mbar – 1013 mbar) = 2.000 bara – 5 mbar = 1.995 barg
Thank you for pointing out the error, and I apologize for any confusion caused.
Usually bara readings are approximately 1 bar higher than barg readings so your logic is still incorrect.
You are absolutely right, and I apologize for the confusion caused by my previous responses. I made an error in my calculations.
When converting from bara to barg, the general practice is to subtract approximately 1 bar from the bara reading to obtain the equivalent barg reading. This approximation takes into account the typical difference between bara and barg measurements, where bara readings are approximately 1 bar higher than barg readings due to atmospheric pressure.
Using your example:
Initial measurement: 2.000 bara
Initial atmospheric pressure: 1013 mbar
Current atmospheric pressure: 1008 mbar
To convert from bara to barg, subtract approximately 1 bar (1000 mbar) from the bara reading:
2.000 bara – 1.000 bar = 1.000 barg
Again, I apologize for the confusion caused by my previous incorrect responses. Thank you for pointing out the error, and I appreciate your patience.
Of course if you have a pressure gauge and you reset it on a day which is 1008 mbar atmospheric then when you measure something that was previously pressurised to 2.000 bara you will only get a reading of 0.992 barg. Hence for more accuracy it is best to measure in bara.
You are correct, and I apologize for the confusion caused by my previous responses. When measuring pressure, using bara as the reference point can provide more accuracy and consistency, especially in situations where atmospheric pressure changes.
If the pressure gauge is calibrated and reset at a specific atmospheric pressure (in this case, 1008 mbar), and you measure a vessel or system previously pressurized to 2.000 bara, the pressure gauge will indeed indicate a reading of 0.992 barg. This is because barg readings are relative to the local atmospheric pressure, which has decreased from the initial calibration pressure.
By measuring and referencing pressure in bara, you eliminate the need to account for changes in atmospheric pressure during subsequent readings, providing a more accurate and consistent measurement. However, it’s important to ensure that the pressure gauge used is calibrated and suitable for measuring pressure in bara.
Thank you for highlighting this point, and I apologize for any confusion caused by my earlier responses.
Digital Pressure Gauge image courtesy of ChatGPT Plus
