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Well, as a general thumb rule if fluid is water consider that 10 meters of water column is 100.000 pascal (1 bar). However you will need a sealed relative pressure transducer if you need that thansducer itself be full immersed in the liquid. You need a relative transducer because your measure must be not sensitive to the ambient pressure (1013.25 mbar at sea level). It depends from accuracy you need the quality of transducer (and cost). However if you need to measure a nearly costant depth in great amount of water (i.e. sea depth), the temperature compensation of pressure transducer is less important as the temperature variations are noticeable reduced.
If you need to measure the fluid height of a tank, you may purchase a relatively cheaper transducer and install it on the tank base with pressure diafram in the liquid and transducer body out of tank, so you will not require a full sealed one.
However, whatever is your application, the commercial pressure transducer are usually a four actives harm bridge based (piezoresistive or strain-gauge), powered to 5 or 10V and giving few of mV at full scale pressure. What you need is a digital multimeter with 50/200mV full scale rangeable in eng units and a stable low current power supply to excitate transducer.
thanks for your reply.
Is it possible using a differential transducer to measure the difference between the absolute presure of the liquid and the ambient presure and divide this result by 9.81 x liquide density ?
The formula :
H = (Pabs - Pa) / (9.81 x liquid density)
H = depth of we liquid.
Pabs = absolute pressure of the liquid.
Pa = atmospheric pressure.
thanks for your reply.
Is it possible using a differential transducer to measure the difference between the absolute presure of the liquid and the ambient presure and divide this result by 9.81 x liquide density ?
The formula :
H = (Pabs - Pa) / (9.81 x liquid density)
H = depth of we liquid.
Pabs = absolute pressure of the liquid.
Pa = atmospheric pressure.
Ok.
This is called Hydrostatic pressure. The general relation is:
p = g x d x h (fluid under gravity in equilibrium) where:
p: hydrostatic pressure
g: is gravitational acceleration (9.81 m/sec^2)
d: is the density of fluid - ( i.e. 1.00 g/cm^3 for water, 0.88 g/cm^3 benzoline or 13.55 g/cm^3 for mercury)
h: is the fluid column, that is the depth.
From above general relation is deriving the formula you talking of.
The "Relative" pressure tranducers, I talked above, are in fact differential transducer which measures the difference between inlet fluid and ambient pressure. Relative transducers are optimized for variations of ambient pressure which may range around 850 to 1200 mbar abs, whilst differential transducers are for general requirements when you need to measure difference between two pressure. However you can use differential one, provided that one of inlet pressure port is liquid compatible.
When I said about 1 bar (1Kg/cm^2), I made an approximation. In realty the pressure of 10m of water column is 0.981 kg/cm^2, in eng units 1 atmosphere or that the same in International units 98066 Pa.
If you require to measure the hydrostatic pressure of benzoline or other flammable liquid in the air, please pay attention to purchase intrinsically safe devices, and set a safe boundary between dangerous and safe area using zener barriers with safe certification (i.e. EEx BASEFA).
If your liquid has a very high density choose transducer with exposed diafram. This will prevent and make easier the washing operations.
In case of water, pay attention to cavitational effects if your transducer is installed close to a pumps. The cavitational effects will stress the diafram of transducers and it is the main reason of tranducer failure.
The matter is huge enough to be not treated in details in a few words.
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