Relation between Pressure and weight

[Megahertz]

I have two questions I would like to ask, if someone can answer them please from their experience or knowledge

1) I would like to know, in hydraulic systems is there any relation between pressure and weight. If I have a pressure sensor which can tell me pressure in BAR and give me 1 to 5 V output for 0-350BAR can I relate it to the weight? If yes, what is the formula or method in doing so?

2) I have seen many sensors advising the output voltage between certain values, lets say 0.5 - 4.5v or 1 to 5v etc. I came across one sensor which tells pressure but the output is stated as 0.5-4.5v regulated. I would like to ask what does this word 'regulated' signifies. Does it simply means 0.5-4.5v volt output based on 0-350 bar pressure or there is something else to it?

[HenrikOlsson]

Hi,
1) Not sure if this is the answer you're looking for but 1Bar is roughly equal to 1kg/cm². So if you have a hydraulic cylinder with a diameter of 50mm and a pressure of 75Bar then the "force" is 25*25*PI*75/100=1472kg.

2) Don't know, sounds like some weird translation. Do you have a link to the particular datasheet?

[Megahertz]

MLH Series PS_008119-7-EN_Final_16Feb11.pdf
Thanks. Here is the datasheet of the sensor I am talking about. It is mentioned towards the bottom - 0.5- 4.5v regulated and others also written the same way.

[HenrikOlsson]

Ah, OK...
The ones with regulated output will have a stable output signal even if the power supply voltage varies. On the ones with ratiometric output the output signals varies with the power supply voltage or in this case with the excitation voltage (I think - haven't looked at it in detail).

/Henrik.

[Megahertz]

Hi,
1) Not sure if this is the answer you're looking for but 1Bar is roughly equal to 1kg/cm². So if you have a hydraulic cylinder with a diameter of 50mm and a pressure of 75Bar then the "force" is 25*25*PI*75/100=1472kg.

1) What about the length/height of the cylinder? Do I only need to know the radius of the cylinder and apply the above formula?

2) What do I do if I have two cylinders in parallel of the same diameter? Do I multiply the result by 2 ?

[HenrikOlsson]

1) Length doesn't matter, only the surface area upon which the pressure works.
2) Yes, If you double the effective area you double the force. It doesn't matter "how" you double the area.

[Megahertz]

HenrikOlsson, thanks a lot for your help.
Just one last question to confirm my understanding.
So, if I have two different diameters for two cylinders, I should calculate the weight individually for each and add it together towards the end to get the total weight.

[HenrikOlsson]

Yes, or calculate the total area and multiply that by the pressure.
If you have one 100mm and one 50mm cylinder you have an effective area of (50*50*pi/100) + (25*25*pi/100) = 78.5+19.6 = 98.1cm²

Just remember that if the cylinders aren't of the same size (diameter) they won't share the load equally (one will "push" more than the other at any given pressure).

/Henrik.