Loadcell Accuracy

Some instrument manufacturers list accuracies as percent of Full Scale (in fact most do) and some as a percentage of reading.

The best way to get this information (since you didn't even include the Model Number of the instrument) is to either RTFM or contact Mettler-Toledo. They actually make money by knowing this information. We don't.

Weight indicator model -- ind 140 mettler toledo i could not find any details for indicator accuracy for mini and max range For example if I go for 1% fsd hear my calibration range is 40 to 1000 kg The results after calibration should for mini range 40 kg --- +/- 9.6 kg for max range --- 1000 kg --- +/- 9.6 My question is that is it feasible for mini range? Now for +/- 2d After calibratuon result should be for mini range 40 kg --- +/-1kg for max range 1000 kg --- +/- 1kg my question is that is it feasible for max range? Hear I can not get any linear reltionship for accuracy of mini and max range.. ax

Your questions are more to do with linearity rather than accuracy. Accuracy and linearity are completely dependant upon the mechanical set-up and the accuracy of the known weights. What degree of accuracy are your known weights are measured to? Any error in these weight values will directly impact the calibration of the head unit. The indicator is only as accurate as the weighing instrument and subsequent calibration.

The only true and accurate method of calibration is by live load testing. I note that you have 1000l tank. Can you accurately measure a volume of water in the tank? After zeroing the tank, fill to capacity and calibrate the span. Empty the tank and re-check the zero. Then put known quantities of water in the tank, say, 20% of capacity, 40% of capacity and so on until full. Check the reading as compared to known volume and you will will get a very precise indication of not only accuracy but the linearity characteristics of the instrument. Remember the instrument is the load cell, the indicator is merely that, an indicator.

Dear philphy,

thanks 4 your response, I am with you whatever you said.

I know the zero and span calibration and I have done it very deeply..

my question is not about the loadcell or weight indicator problem.

I want 2 know what are the acceptable readings i should get after calibration.

at the time of verification

what are my acceptable limits

at mini range /-- 40 kg ----- what +/- kg i should get

at max range 1000 kg ----- what +/- kg i should get for accurate measurement....

Now I am a little confused. your acceptable limits should be within the accuracy guarantee of the instrument. If it is rated @ 1%, then at 40kg = +/-0.4kg, 1000kg=+/-1kg. Unless the manufacturer has a disclaimer that accuracy will be impacted at lower end of measurement then the instrument should be linear and exihibit the same accuracy over the entire range.

Because the indicator displays in 0.5kg you will have problem at the lower end. The indicator will show 0.5kg as soon as the weight is more than 0.3kg and probably indicate 0kg under 0.3kg. depending on resolution the indicator may in fact show 0kg at 0.4kg.

http://www.cannamdo.com/upload/Tai%20lieu/IND140_Technical%20Manual.pdf

Also what is the load cell capacity? Use this formula:

Minimum Increment size

= ( LC Capacity x Ratio x uV per incement ) / ( cell output x excitation )

Load cell output is rated in mV/V (millivolts per volt of excitation), marked on

load cell data tag. METTLER TOLEDO load cells are typically 2 mV/V. Other load

cells can range from 1 mV/V to 3mV/V; The load cell capacity is the rated

capacity marked on load cell data tag. The ratio is the total number of load

cells in the system or the total lever ratio (if scale is a mechanical lever system

conversion).

Sample Calculation

Refer to the following example of mV per increment calculation for a hopper

scale installation.

�� Load Cell Capacity 2500 kg

�� Number of Load Cells 4

�� Load Cell Output 2mV/V

�� IND140 Excitation Voltage 10 VDC

�� IND140 Minimum Input Signal per Increment 1uV/Inc

Use the following formula to calculate the minimum increment size:

Minimum Increment size

= ( LC Capacity x Ratio x uV per incement ) / ( cell output x excitation )

Substituting this hopper scale parameters in the formula:

Minimum Increment Size

= ( 2500 kg x 4 load cells ) / ( 2 mV/V x 10V / 1 uV )

= ( 2500 kg x 4 load cells ) / 20000

= 0.5 kg

I agree.

hear you have mentioned +/-1 % from whuch standard norm you have taken this

all things are ok on their place

now my question is that what I should kept as standard aceeptance limit for this display

for all etire operation range

at 40 kg

at 100 kg

at 200 kg

at 500 kg

at 800 kg

at 1000 kg

pleade provide acceptance limit for this readings as per standards

as far as i remember the reading should be in range according to accuracy class
so if you are after that (telling/finding out to what class your weighing corresponds)
then . . . it's all about the overall system setup AND the specified equipment capabilities

put on a 500kg test mass and look at temerature response. You may have a curve to overlay.

Contact Mettler Toledo, they will have the exact parameters of accuracy and calibration requirements for your equipment.

Under normal conditions accuracy will be in the range of 0.25% to 1% and the calibration weights have to be 100% precise.

The big question here is what accuracy you really need. On 1,000 Kg a 1% or 10 Kg change is barely appreciable, so adapt to your true needs.

3000 divisions is pretty easy for even a low cost floor scale. However when dealing with tank you have to minimize the binding forces of the connections and the load cell mounts.

1) Even a flex connection has a bind, just not as much.

2) you can not zero out the full effects of a connection.

The pdf under the downloads section of this page goes into all the theory and construction tips. Page 37-42 show best practices

http://www.dataweigh.com/products/rice-lake/1700-he-tank-mount/