Here we go over if you can use a single load cell to measure constant weight, different types of load cells, the different designs of load cells and a lot more.

1. Phone Number: 1-800-550-0280
Contact Email: contact@tacunasystems.com
Website: https://tacunasystems.com/
Load Cell Weight
CAN YOU USE A SINGLE LOAD CELL TO
MEASURE CONSTANT WEIGHT?
A load cell is an instrument that helps to determine the size of a load (either
a force or a weight) and can also give the direction to which the load is act-
ing.
Technically, a load cell is a sensor that detects changes in a physical stim-
ulus (in this case, a force, weight or pressure) and then produces an output
proportional to the physical stimulus. Therefore, for a certain constant load
or weight size, the load cell gives an output value that is proportional to the
magnitude of the weight.
Types of Load Cells
In order to measure a constant weight or any loads size using a single load
cell, there are wide varieties of options available. There are different types
of load cells, each for various applications.
The most commonly used types are:
 Strain gauge load cell
 Capacitance load cell
 Hydraulic load cell
 Pneumatic load cell
The first two types (strain gauge and capacitance load cell) are electrical
transducer devices. An electrical transducer is a sensor that detects a

2. physical stimulus and then produces an electrical analog signal (voltage) as
its output. The other two devices (hydraulic and pneumatic load cell) do not
directly produce output as electrical signals but they can have their output
transduced by other means depending on the application requirement.
The most widely used type among all load cell types is the strain gauge
load cell. This device can be found in all industries such as medicine, auto-
mation, automotive, domestic etc. hence, to measure a constant weight us-
ing a load cell, you will have a wide variety of strain gauge types to choose
from. The advantages of this type will be seen in the latter sections of the
article.
The Design and the Mode of Opera-
tion of the Load Cells
The decision to use a single load cell to measure a constant weight over a
period of time will require that the operator or user understands a little bit of
information and details on how these stuff work.
Understanding the design and the mode of operation of these load cells will
influence the decision on which type of load cell fits your requirements for
determining the size of a certain weight.
1. Hydraulic Load Cell
 This type of load cell is a force-balance device. Its components are
housed in a cylindrical frame made of stainless steel. Design The fig-
ure below shows a general arrangement of a hydraulic load cell. The
device consists of the following parts: Figure 1. The Hydraulic load
cell
Figure 1. The Hydraulic Load Cell

3.  A Diaphragm: This is an elastic material or in the form of a corru-
gated plate.
 The Loading Surface or Platform: This is usually a piston that is
designed as a loading platform to which the diaphragm is bonded.
The diaphragm is attached to the base of this piston to make con-
tact with the hydraulic fluid.
 The Hydraulic Fluid: The device is filled with oil or at times water.
 A Pressure Output: This might be a pressure gauge that is con-
nected to the load cell through a bourdon tube. The Mode of Oper-
ation To measure a weight with this device, the weight is placed on
the loading platform.
The oil-filled chamber is connected to a pressure gauge and sealed
by the diaphragm, hence, this applied weight will produce pressure
increases in the confined oil. This is then indicated on the pressure
gauge. As mentioned earlier, if you wish to obtain the output in the
form of an electrical analog form, then the output can be trans-
duced using a pressure transducer in place of the pressure gauge.
It should be noted that the hydraulic load cells are stiff with a force
range of up to 5MN and a system accuracy in the order of 0.25 to
1.0 percent.
2. The Pneumatic Load Cell Design
 The device consists of the following parts that are similar to those of
the hydraulic type. The figure below shows a general arrangement of
a pneumatic load cell.
Figure 2. A Pneumatic Load Cell

4.  The Loading Platform: This is the surface on which the weight to be
measured is placed
 An Elastic Diaphragm: It is elastic in nature and made up of a
flexible material or can be made corrugated
 The Air Supply Regulator: This part is always located below the
diaphragm or at the bottom of the load cell. This air supply regula-
tor is simply an opening that is regulated by a valve.
 An Outlet Nozzle: This is an opening that does not have a direct
valve that regulates it.
 The Flapper: This is also called the bleed valve. It is attached to
the bottom of the loading platform together with the diaphragm. Its
movement closes or opens the outlet nozzle.
 A Pressure Output(Manometer): This indicates the pressure as a
measure of the weight or applied force. The Mode Operation The
weight to be measured is placed on the loading platform. This then
goes to exert a certain amount of pressure on the air inside the
confined space as the diaphragm deflects.
The deflection of the diaphragm and the increased internal air pres-
sure causes the flapper to move downwards and shut off the outlet
nozzle. This then balances the internal pressure and the resultant
pressure causes the deflection of the dial in the pressure gauge.
This amount then equals a value that is proportional to the actual
weight size.
This proportional constant is easily obtained by initially calibrating
the load cell using a known weight. To return the diaphragm to its
pre-loaded position, the air supply regulator is used, this device can
hold load up to 25KN. A pressure transducer can also be fixed at
the output so as to obtain an electrical analog output signal.
3. Capacitive Load Cell Design
 Capacitive Load Cell Design The basic design of a capacitive trans-
ducer is shown in the figure below
 A Stationary Plate: This is one of the two parallel plates and it is
attached to the body of the insulated housing.
 A Moveable Plate: This is the second of the two parallel plates
and it changes position under the influence of the weight. So the
conventional design has a loading platform that is attached directly
to this movable plate.

5.  The Dielectric: This is situated between the two parallel metallic
plates. It is often made to be air, but can also be other elements or
materials.
 The Insulated Housing: This provides the support and protection
for the parts of the capacitive load cell The Mode of Operation The
construction of the devices ensures that the two parallel metal
plates are separated by a distance filled with a dielectric. A load or
weight to be measured is then applied to the movable plate which
deflects under this influence. This deflection then decrease the dis-
tance between the two plates, while the area of the plates and the
dielectric remains constant.
The relationship between the device’s capacitance, the distance
between its plates, the area, and the dielectric can be further un-
derstood by this mathematical formula below. Where C is the ca-
pacitance, is the relative permittivity, is the absolute permittivity, A
is the cross-sectional area of the capacitive plates and d is the dis-
tance between the plates.
This change in distance causes a change in capacitance, this can
then be measured by using a Wheatstone bridge (Wien Bridge) or
through the resonant circuit of an oscillator. The capacitance
causes a voltage to be stored in the capacitor’s electric field, this
voltage can also be amplified to indicate the capacitance of the de-
vice. Whichever method through which the capacitance is obtained,
it shows the equivalent size of the weight that produced the capaci-
tance. Therefore, a constant weight placed on a capacitive load cell
will produce a constant value of capacitance.
The value might change or vary within a certain range that depends
on the accuracy of the device. Generally, capacitive load cells are
very sensitive and they can measure static weight changes as well
as dynamic changes. A resolution of about can be obtained.
4. Strain Gauge Load Cell Design
 The Elastic Element: : This is the part of the load cell that trans-
duces the applied weight into a strain, in a proportion to the weight.
Hence, it is called the primary transducer. This part makes up a large
visible percentage of the load cell’s body and it is called the structural
member. Generally, the geometric shape of this element determines

6. the category to which the strain gauge load cell belongs. For exam-
ple, a geometric shape in the form of a beam makes a beam strain
gauge load cell. Furthermore, the geometric shape and the modulus
of elasticity of this element govern the weight the lad cell can hold in
a particular direction and the overall performance of the device.
 The Strain Gauge: This is a length of a conductor (metallic or
semiconductor), which is first micro-machined on a polyester back-
ing or a non-conductive layer to form a composite. The composite
is then bonded to the elastic element in such a way that it receives
a sufficient amount of the strain along the direction at which the
weight is placed.
Figure 3. The Strain
gauge Load Cell.
 The strain gauge transduces the transduced strain into a proportional
change in its electrical resistance. Hence, the strain gauge is the sec-
ondary transducer. The strain is directly proportional to the applied
weight, hence, the change in the resistance is therefore equivalently
proportional to the weight. This change in electrical resistance is then
measured to indicate weight. So, when the strain gauge is subjected
to a strain, its length, area and electrical resistance changes in ac-
cordance to this formula: Where R is the electrical resistance, is the
resistivity of the gauge material, L is the length of the conductive
strip, A is the cross-sectional area of the conductive strip. The strain
gauge and the elastic element must be able to hold the constant
weight for a period of time without breaking or exceeding their elastic

7. limit. There are different types of strain gauges that offer unique char-
acteristics and they include the wire strain gauge, the thin-film strain
gauge, the foil strain gauge and the semiconductor strain gauge.
 The Housing Unit: This forms the protective casing of the whole
load cell against unfavorable environmental conditions. It allows for
external fixings such as mounting kits and screws to be attached to
the load cell.
View These Types of Load Cells:
Double Ended Shear Beam
Disk Load Cells
S-Type / S-beam
The Mode of Operation
The weight to be measured is placed on the load application point of the
load cell. The weight is transduced into strain by the elastic element, and
the transduced strain is further transduced into a change in electrical re-
sistance by the strain gauge as its dimensions changes under the influence
of the strain caused by the weight.
The change is electrical resistance is then measured by using a Wheat-
stone bridge. If there are more than one strain gauges used, they are incor-
porated in a Wheatstone bridge circuit configuration to measure their col-
lective change in resistance.
Therefore, it is the output of the Wheatstone bridge that forms the output of
the strain gauge load cell. This output is in the form of an electrical analog
voltage usually of the order of millivolts (mV).
A Wheatstone bridge has four arms, hence it can hold up to four strain
gauges. The number of strain gauges on the arms of the bridge determines
its configuration. A single strain gauge load cell will use the quarter-bridge
configuration. A double strain gauge load cell will use the half-bridge con-
figuration. A four strain gauge will use the full-bridge configuration.

8. Figure 4. A Full-Bridge Configura-
tion
The strain gauges acting the same direction (compression or tension) are
placed in opposite arms of the bridge so as to maximize the response of
the load cell.
Furthermore, to increase sensitivity (the rate of change of the output volt-
age with respect to the change in length) and also obtain accurate results,
it is advised to get a load cell with more than one strain gauge.
Calibration of the Load Cell
Calibration is the comparison of the reading of the instrument in question
(the load cell to be used for measuring the constant weight) to a known
standard and the maintenance of the evidentiary chain from that standard.
Technically, it is called the Tractability.
The process of calibration helps to eliminate the errors that are inherent in
the load cell. These errors are called the systematic errors. Calibration at
sufficient intermediate points in the range of an instrument can help cover
systematic non-linearity.
Also, microprocessor–based implementation of the whole measurement
setup will reduce this same problem of systematic non-linearity. This is so
because microprocessors can perform multipoint breakpoint linearization.
The load cell performance is influenced by other quantities such as temper-
ature and even a change in the direction of measurement, hence constant
calibration is needed. A formal calibration of the load cell [used for constant
weight measurement] should be carried out at intervals of about 1-2 years
to maintain accurate results.

9. Use: Calibration services at Tacuna Systems or check out our load cell cal-
ibration weights.
Load Cell Specifications
The specifications of a load cell can easily be obtained from the manufac-
turer by asking for a datasheet. These specifications are of great im-
portance when it comes to the accuracy of the load cell in providing a relia-
ble result for a constant weight measured over a period of time.
These specifications include:
 The Zero Balance: This is the default output signal of the load cell
when no weight is placed on it. When using a load cell, you can eas-
ily confirm this value by taking the output reading when all weights
(including dead load) has been removed
 Non-Linearity: Normally, the output of the load cell is meant to be
exactly proportional to the weight (at least form some intervals). How-
ever, in practical measurements, there are discrepancies and this
called the non-linearity error. Non-linearity expresses the maximum
deviation of the true input/output curve from the idealized straight line
approximating it.
 Hysteresis: This is the difference between the outputs of a load cell
as the weight is increased [from no load to the full rated capacity] and
the output of a load cell as the weight is decreased [from the full
rated capacity to no load]. For a constant weight application, this
specification will not affect the result accuracy but it should still be
taken into consideration.
 Non-Repeatability: This is the maximum difference between the out-
puts of the load cell for repeated loading under the same conditions.
For a constant weight application, this should also not affect the ac-
curacy of the measurement.
 Creep: This is the most important specification to pay attention to
when it comes to a constant weight application. Creep depicts the
change in the load cell output with time under a constant load and
with all the environmental conditions being constant. This simply
means that if you leave a constant weight on the load cell, the output
reading changes by a certain percentage even though no weight is
being added or removed.
 Temperature Effects on The Zero Balance and the Output: Tem-
perature shifts affect the zero load position and the output of the load
cell. Strain gauge load cells implore various effective temperature
compensation techniques to cater for this effects.

10. Conclusion
It can then be concluded that it is possible to use a single load cell to meas-
ure a constant weight over a long period of time. However, the accuracy of
the output results will be based on the type of load cell you chose and the
specifications of the load cell.
Also, the strain gauge load cell is the best type of load cell and it is the
most suited for all types of applications, hence it is used widely in all indus-
tries.
Source
 The Instrumentation Reference Book Edited by Walt Boyes, Fourth
Edition
 The Essential Guide to Load Cells
 Force and Weight Measurement Resources
 What is the Material Used in Commercial Load Cells?
 Tacuna Development
Phone Number: 1-800-550-0280
Contact Email: contact@tacunasystems.com
Website: https://tacunasystems.com/