ASTM D5190 Vapor Pressure of Petroleum Products (Automatic Method)
ASTM D5190 Standard Test Method for Vapor Pressure of Petroleum Products (Automatic Method)
10. Calibration
10.1 Pressure Transducer:
10.1.1 Calibrate the pressure transducer at least every 30 days or when needed as indicated from the performance checks. The calibration of the transducer is accomplished using three reference materials to cover the range above and below 34 kPa (5.0 psi).
NOTE 4 - The instrument manufacturer provides an alternative calibration procedure using two reference points, zero pressure (<0.1 kPa) and the ambient barometric pressure. However, since this procedure was not included in the interlaboratory program, the precision and bias can be affected by its use.
10.1.2 Load n-hexane into the instrument, obtain a vapor pressure reading and then adjust the zero potentiometer for the transducer to obtain a calibration value of 5.00 +/- -0.02 on the digital meter display.
NOTE 5 - The target calibration values used in this section are specific to the automatic vapor pressure instrument evaluated in the 1988 interlaboratory cooperative program. These calibration values do not necessarily correspond to the total vapor pressures or the dry vapor pressures (see Test Method D4953) reported for the reference calibration materials, but rather are values that the instrument manufacturer suggests using to produce a dry vapor pressure equivalent reading on the digital display.
10.1.3 Load n-pentane into the instrument, obtain a pressure reading on the digital meter, and then adjust the transducer span potentiometer to achieve a value of 15.40 +/- -0.05 on the digital meter.
10.1.4 Repeat 10.1.2 and 10.1.3 until the appropriate calibration values are displayed without making further adjustments.
10.1.5 Load the instrument with 2,2-dimethylbutane and obtain a pressure reading. If the digital display reads 9.90 +/- 0.1, then the instrument is calibrated; if not, then repeat the above procedure until a satisfactory calibration is achieved.
10.1.6 For calibration of the range below 34 kPa (5.0 psi), perform the steps in 10.1.2 to 10.1.4, replacing n-hexane (34 kPa) in step 10.1.2 with toluene (7 kPa), and replacing n-pentane (106 kPa) in step 10.1.3 with n-hexane (34 kPa).
10.2 Temperature - At least every six months, check the calibration of the thermometer used in the thermostatically controlled bath against a National Institute of Standards and Technology (NIST) traceable thermometer and check the capability of the bath thermostat control to maintain a temperature of 37.8 +/- 0.1°C (100 +/- 0.2°F) throughout the measurement period. Take corrective actions when the thermometer and thermostat exceed the limits stated.
11. Quality Control Checks
11.1 Use a verification fluid with known volatility as an independent check against the instrument calibration each day the instrument is in use. For pure compounds (see 7.1 and Note 1), multiple test specimens may be taken from the same container over time, provided the pure compound is air saturated according to the procedure given in 8.4 and the spent test specimens are not re-used, in whole or in part. Record the dry vapor pressure equivalent value, and compare this to the statistical value of the control sample from your laboratory. If the difference exceeds your control limits, check the calibration of the instrument.
11.2 Some possible materials and their corresponding vapor pressures, as found in ASTM DS4B, include: cyclopentane, 68.3 kPa (9.91 psi); 2,2-dimethylbutane 68.0 kPa (9.86 psi); 2,3-dimethylbutane 51.1 kPa (7.41 psi); 2-methylpentane 46.7 kPa (6.77 psi); and toluene 7.1 kPa (1.03 psi).
NOTE 6 - It is recommended that at least one type of control sample used in 11.1 be representative of the fuel(s) regularly tested by the laboratory. The total vapor pressure measurement process (including operator technique) can be checked periodically by performing this test method on previously prepared samples from one batch of product, as per procedure described in 8.1.2. Samples should be stored in an environment suitable for long term storage without sample degradation. Analysis of result(s) from these quality control samples can be carried out using control chart techniques or other statistically equivalent techniques.
