Hydraulics and Weight Measurements

I think you've already answered your own question...

Using a pressure transducer tee'd in as you say will measure the pressure in the pipeline and knowing the cross-section area of the lifting device you will have the weight of the item being lifted!!

John.

"you will have the weight of the item being lifted!!" + or - the force if it is accelerating, not sure if you were after the weight being lifted or the force on the hydraulics.

Cory

Are you only interested from i visual point of view or is it to signal another component

This is guest #0. Thanks, fellas, for replying, and permit me to consolidate my response, if you will.

Electroman: John, so if I read you correctly, I must find a transducer(s) and tee it in somehow to the pressure lines feeding the cylinder. The transducer will act as a sender, of the dynamic hydraulic pressure (the piston and load resistance imparted) in either or both pressure lines--assuming weight measurement in up and down directions, and powered lowering of the load (?); the receiving "box" or instrument will be calibrated to convert and display the force measured, in weight units. Is that the idea? Can you suggests sources for either the sender and/or the calibrate-able receiving units? Another question: if the fluid conduit in which pressure is measured is smaller-diameter relative to the piston diameter, will a secondary calculation be required to convert pressure in the conduit (and at the transducer port) so as to measure force (line psi/piston si) in the greater-diameter cylinder? If so, what conversion factor could be used? (Please forgive if this question is ill conceived.)

Guest #3: Cory, I am not exactly sure, as yet, about whether the sytem would measure static or dynamic loading; or how it might do both. (There is a human factors and productivity consideration that might have to be taken into account.) Presently the "lift/lower" operation goes something like this. The human operator grasps a "heavy" container (the tare of which can be determined). He then lifts the container (during which weighing would begin). for about 3 - 6 seconds, to a height of about 10-12 feet. Next, he lowers the (now empty) light container (the tare weight) to the ground--typically no less slowly, and sometimes more quickly, than it was lifted initially. So, it would seem that either the operator would need be trained to halt the lift and lower actions momentarily in order to get stabilized (i.e., static) weights; or the system might be "aligned" somehow to compensate for (or ignore) acceleraton forces? One thing that might work, seems to me, is a receiving unit that could simply latch and display the least-weight measurement during each load movement motion. (Something analogous to a dual tube, max-min thermometer?) When the weight became zero or negative (the container is on the ground) the receiving unit would reset. What do you think of this, or any alternative, approach--and as to how getting the actual load measurement (or something fairly close) could be implemented?

Guest #2: Seems to me that the visual...even strictly analog...would be the simplest starting point; but a remote--and, sooner or later, digital--display would almost certainly come about at some point. I can even envision the measurements being provided, not only to the operator, but also to a local or remote "data" recording facility...so that accumulated statistics could be compiled for productivity and analysis purposes. But, for purposes of discussion at this point, let us say that the readout display will be at an instrument separate from the sensor--that a mere gauge fitted to the hydraulic line won't fit the requirement. Perhaps later, after a rudimentary system is drawn up, we can talk more about additional enhancements and interfaces for the readout instrument.

Gentlemen: Thank each of you and I look forward to more of your insightful inputs.

Stephen

Hydrostatic load cell weighing technology has been around for a long time. However the cells will weigh the acceleration forces just as accurately as the static load. If the movement is smooth you should be somewhat accurate.

One good manufacturer of the load cells is Emery Winslow.
Click http://www.emerywinslow.com/index.html

Regards, Delmar Schmidt
Melfi Technologies Houston
www.melfitechnologies.com

If you use a pressure transducer in the lines, asside from dynamic effects, you will need to take into account seal friction of the lifting jack. This may be predictable but likely to give more error than the 5 lb you are looking for.

Using load cells is definetely the answer. Check the sites below, they may already have or create a system for you.

http://www.musemeasurements.com/About.htm

http://www.ricelake.com/

I gather the system you have described works like this.

1/. Operator load barrel on lift.

2/. Operator starts hydraulic lift to raise barrel

3/. Barrel is drained

4/. Operator releases hydraulic lift allowing empty barrel to return to initial level.

The problem with the system is that to raise the barrel the pressure in the hydraulic system need to be greater than the weight of the barrel divided by the cross section of the hydraulic ram. The only reason the barrel stops at the top is probably not due to the hydraulic pressure reducing but rather the ram reaching an end stop.

On the way down the pressure is released and will be less than the weight of the barrel/area and again the reason it stops is it reaches the end stop.

As you correctly said the only way the use the pressure to measure the weight of the barrel on the way down would be to get the operator to stop it sometime during the lowering process and allow the pressure to stabilize.

The same would be true on the way up. To use the pressure in the hydraulic system to indicate the weight would require the operator to stop the raising process and allow the pressures to stabilize.

I don't know if is practical to stop the process both on the way up or down for a couple of seconds but if it is then the pressure could easily be used to indicate the weight of the barrel. If not I would agree with what others have said and look at some sort of separate load sensing system.