The Gas Pressure – Differential Sensor is a relative pressure sensor. The sensor has two ports for pressure measurement, for identification purposes the ports are labelled P1 and P2. The pressure measured is the difference between the pressures applied to these ports. For example, a pressure of 10 kPa to port P1 and a pressure of 10kPa to Port P2 would give a pressure reading of 0 kPa. You can seal off either port to create a single port pressure sensor; in this condition the pressure measured will be relative not absolute.  

If both ports are left open to the atmosphere, the effect of atmospheric pressure will equal each other out and the difference between the ports will be zero.  

If only one port is left open to the atmosphere and the other sealed, the sensor will measure pressures above or below atmospheric pressure i.e. gauge pressure. If the sensor shows a reading of 25 kPa (gauge), that is 25 kPa above atmospheric pressure. Since atmospheric pressure is approx. 101.3 kPa, the equivalent atmospheric pressure reading would be 25 + 101.3 = 126.3 kPa (absolute). The calculate tool can be used to create a new channel of data with the atmospheric pressure value added in. This would be useful when using the sensor to record the small changes of pressure when attempting to estimate absolute zero. In the estimation of absolute zero you must use absolute pressure and absolute temperature (Kelvin). 

The maximum pressure between ports P1 to P2 that this sensor can tolerate without permanent damage is: 200 kPa  

Investigations that would traditionally use a manometer can use this sensor.  One port is connected to the ‘living’ chamber that holds the organisms. The other port is connected to a ‘non-living’ chamber which acts as a thermo barometer. CO2 given off by the respiring organisms would be absorbed by potassium hydroxide, resulting in a change of pressure.    

  • The barb on the Luer connectors supplied with the Gas Pressure sensors will fit PVC or Silicon tubing with an internal diameter of 3 mm (1/8”). 
  • A Gas Pressure Accessory Kit, Product No.1149, is available which contains a selection of tubing elements and connectors which allow gas tight connections to the Gas Pressure sensors and connected apparatus.  
  • Only use these sensors to measure non-corrosive/non-ionic media such as air or dry gases.  
  • This sensor is not suitable for use with flammable gases. 
  • A small amount of appropriate lubricant on the male Luer end will let tubing slide on more easily. 
  • The vapour pressure of liquids can be monitored, but do not allow liquid to enter the sensor. A small plug of cotton wool in the tubing going to the sensor is recommended.
  • Protect from the weather – keep the sensor dry. 
  • The container used with the Pressure sensor must be suitable for the task and able to sustain the pressure changes. The type of container selected will depend on the investigation. 
  • Gas contained in a system under pressure will try to find a way out. The longer the investigation lasts, the more dominant the effect of any leaks will become - try to complete the investigation as quickly as it allows. 
  • The sensor is not waterproof. It may be cleaned using a damp cloth. Do not immerse in water or detergent. Do not place the sensor in an environment in which high humidity levels are possible as this may result in damage or malfunction. 

Units of Measurement

Pressure is defined as force per unit area and the standard SI unit of pressure is the pascal (Pa).

The conversion from kPa to mBar is simply to multiply by 10. (1 kPascal = 10 millibar = 0.14504 psi).

1 Pascal = 1 Newton per square meter (1 N/m2).

Equivalent values for 1 atmosphere (atm) are = 101.325 kPa = 760 mm Hg = 29.92 in. of Hg (at 0oC) = 14.70 psi = 1013 millibar.