EU RO Mutual Recognition Group

General description of the product

Pressure gauges/transmitters are electromechanical devices (typically stainless steel or ceramic diaphragm) suitable for marine use. It is used to deliver pressure information locally or to a remote position.

The conversion of pressure into an electrical signal is achieved by the physical deformation of strain gages which are bonded into the diaphragm of the pressure transducer. Pressure applied to the pressure transducer produces a deflection of the diaphragm which introduces strain to the gages. The strain will produce an electrical resistance change proportional to the pressure.

Generally, there are three different types of electrical output available:

i) Millivolt Output - Pressure Transducers: The output of the millivolt transducer is nominally around 30mV. The actual output is directly proportional to the pressure transducer input power supply or excitation. If the excitation fluctuates, the output will change also. Because of this dependence on the excitation level, regulated power supplies are suggested for use with millivolt transducers. Because the output signal is so low, the transducer should not be located in an electrically noisy environment. The distances between the transducer and the readout instrument should also be kept relatively short.

ii) Voltage Output - Pressure Transducers: The output is normally 0-5Vdc or 0-10Vdc. Because they have a higher level output these transducers are not as susceptible to electrical noise as millivolt transducers and can therefore be used in much more complicate environments.

iii) 4-20 mA Output - Pressure Transducers: Since a 4-20mA signal is least affected by electrical noise and resistance in the signal wires, these transducers are often used when the signal must be transmitted to long distances. It is not uncommon to use these transducers in applications where the lead wire must be a few hundred meters or more.