C186 – Pressure Calculation – Absolute and Gauge
Description
This calculates pressure generated either using a pressure balance (dead weight tester) as the standard or a digital pressure indicator or gauge. Where appropriate the equation can be solved for either pressure or mass to generate pressure.
References
Kelton calculation reference C186
KIMS calculation reference K200
FLOCALC calculation reference F018
This replaces calculation C130/K120
Options
Pressure Mode
- Absolute
This option enables the use of a reference pressure, for example, absolute pressure indicating instruments can be calibrated by generating gauge pressure using a dead weight pressure and adding a reference pressure which is equal to barometric pressure. If this is selected make sure that pressure input is set to use absolute pressure units.
- Gauge
If gauge mode is selected the reference pressure is taken to be 1 atmosphere.
Reference standard
- Dead weight tester – ‘mass and effective area’ method
Use this option if you are generating pressure using a dead weight tester (pressure balance) which is calibrated to give values for mass and effective area.
- Dead weight tester – ‘Kn’ method
Use this option if you are generating pressure using a dead weight tester (pressure balance) which is calibrated to give the mass pressure ratio Kn.
- Dead weight tester – ‘pressure’ method
Use this option if you are generating pressure using a dead weight tester (pressure balance) using a nominal value with corrections.
- Digital pressure indicator or gauge.
Use this option if you are generating pressure using other methods, for example, a digital pressure indicator or gauge.
Output Type
- Digital
For this option the output is in pressure units
- Analogue
Fot this option the output is converted to a voltage or current.
Calibration Correction
- Apply
Select this option to apply a correction to account for values obtained through laboratory calibration, for example a foot-print calibration of a differential pressure transmitter.
Correct For
- Head
If selected, the head correction is added to the calculated pressure output.
| Where | ||
|---|---|---|
| ρ | = | The density of the pressure transmitting fluid |
| g | = | The local value for acceleration due to gravity |
| h | = | The height of the tester above the instrument being calibrated |
- Temperature
If selected, allows the user to input values for Piston/Cylinder temperature, Calibration temperature and Temperature coefficient.
- Density of air
If not selected, the default value is 1.2kgm-3.
- Density of mass
If not selected, the default value is 8000 kgm-3.
- Surface Tension
If not selected, the default value is 0 N.
- Buoyancy
If not selected, the default value is 0 N.
- Gravity
If not selected, the local gravity is taken as 9.80665ms-2.
Calculations
Dead Weight Tester – ‘Mass and Effective Area’ Method
- Solving for Pressure
This equation calculates the pressure generated by loading a piston with mass.
- Solving for Mass
This equation calculates the applied mass required to generate pressure.
| Where | ||
|---|---|---|
| m | = | Mass |
| Pr | = | Residual Pressure; this will typically be barometric pressure or the bell jar pressure for an absolute DWT |
| P | = | Pressure |
| ρa | = | Density of Air |
| ρm | = | Density of the Mass |
| σc | = | Force due to Surface Tension |
| B | = | Force due to Piston Buoyancy |
| gl | = | Local Gravity |
| Ao | = | Effective Area |
| α | = | Pressure coefficient |
| λ | = | Temperature coefficient (the combined temperature coefficient of the piston cylinder unit ap + ac) |
| tc | = | Calibration temperature |
| t | = | PC temperature |
Dead Weight Tester – ‘Kn’ Method
- Solving for Pressure
This equation calculates the pressure generated by loading a piston with mass.
- Solving for Mass
This equation calculates the applied mass required to generate pressure.
| Where | ||
|---|---|---|
| m | = | Mass |
| Pr | = | Residual Pressure |
| P | = | Pressure |
| gl | = | Local Gravity |
| gc | = | Calibration reference gravity |
| Kn | = | Pressure ratio |
| α | = | Pressure Coefficient |
| λ | = | Temperature Coefficient (the combined temperature coefficient of the piston cylinder unit ap + ac) |
| tc | = | Calibration Temperature |
| t | = | PC Temperature |
Dead Weight Tester – ‘Pressure’ method
| Where | ||
|---|---|---|
| Pr | = | Residual pressure |
| gl | = | Local gravity |
| gc | = | Calibration reference gravity |
| λ | = | Temperature coefficient (the combined temperature coefficient of the piston cylinder unit ap + ac) |
| tc | = | Calibration temperature |
| t | = | PC temperature |
Digital Pressure Indicator or Gauge
For this option the generated pressure is taken to be that which is indicated on the standard corrected for head where applicable.