**Name of Standard: **National standard of pressure differentials

**Code designation:** ECM 170-6/08-037

**Year of publication:** 2008

**Department:** nr. 6013 CMI RI Brno

**Guarantor:** Ing. Richard Páviš

**Number of CMC lines provided**: 1

Mode | Range | Uncertainty(k = 2) |

Differential pressure | 100 Pa – 1 MPa | 1 Pa + 5∙10^{-5}∙p |

(under static pressures up to 20 MPa)

(p is the value of the generated pressure in pascals)

*CMC magnitudes are expressed in terms of expanded uncertainty using an expansion factor of k = 2 (coverage probability of approximately 95%).*

The basis of the standard is a pressure divider, i.e. a set of three coaxial pistons. The spaces below and above the middle piston are filled with gas at the required static pressure. The lower one is connected to a piston pressure gauge operating with an oil medium, which generates a pressure that is divided by the ratio of the effective areas of the divider pistons. Since the effective area of the middle piston is nominally 101 times larger than that of the upper and lower pistons, the ratio of the hydraulic and differential pressures (division ratio) is nominally equal to 100.

The differential pressure generated by the national standard is calculated according to the definition equation:

Where stands for:

| differential pressure, |

| deformation coefficient of the piston-cylinder, |

| coefficient of thermal expansion of the piston-cylinder, |

| the mass of the additional weight, |

| local acceleration due to gravity, |

| the pressure generated by the oil pressure gauge, |

| coefficient of thermal expansion of the piston-cylinder, |

| air density, |

| density of weights, |

| temperature at initial equilibrium, |

| the size of the effective area of the piston-cylinder at zero pressure and reference temperature. |