Force Gauge / Digital Force Gauge

For quick, easy and accurate force measurements, manufacturers rely on PCE’s force gauge products. A force gauge is a valuable tool used to measure product performance, safety and quality as well as compliance with industry standards. A force gauge also is used to evaluate the physical and mechanical properties of raw materials and components during product research, development, design, manufacturing, production and assembly. Thus, a force gauge has many uses including but not limited to testing of plastics, packaging, paper, medical devices, electronics, fabric, textiles, springs, wires, electrodes, welds, metals and material composites.

A force is usually visible only when it causes changes. We do not see the force though, but its effect. However, this effect is not only dependent on the height and direction of the force, but also on the influences that counteract the force. In order to be able to determine and compare forces objectively, various methods and devices for measuring forces have been developed. In a force gauge with an analogue display, a pointer is usually moved along the scale by the force to be measured. The force gauge with a digital display shows the measured values as a graph or numerical value on the electronic display. Many of these devices can also store the measured data available in the electronic form or transmit it directly to computers or other devices via interfaces.

The internationally used unit for force is the newton. It also applies to the weight force caused by the gravity. In everyday life, in medicine and also for load specifications, however, the term weight is usually used with the specifications in the unit kilogram and other forces are also specified in kilograms. For this reason, there are many models of force gauges that display the measured values in grams or kilograms. In the Anglo-American language area, the force reference is indicated by an appended f for force, where it is not kg but kgf. A force of one kilogram (kg or kgf) corresponds to about 10 (9.81) newtons and one newton to about 100 (102) grams. The measuring range, the display steps and the measuring accuracy depend on the measuring principle and the force transducer used. For example, a digital force gauge of a certain model series can measure from 0.000 to 5.000 Newton with a resolution of 0.001 Newton and another force gauge of the same model series can measure up to 100,000 Newton with a resolution of 10 Newton.

The force gauge can be destroyed by the forces that are too high, but also by incorrect loading with the wrong force application point, wrong force direction or by additional dynamic loads that have not been taken into account. The magnitude and direction of the forces and whether they can be safely absorbed and evaluated by the measuring device therefore play an important role in the selection of the device. In addition, it must be taken into account that many of the devices only function reliably if certain operating conditions are observed. For some applications there is a large selection of different types of devices, but for the others only a few device variants come into question or special adaptations or special solutions have to be developed for the individual case.

How do you determine what force gauge is best suited to your application? The following text is designed to help you make an informed purchasing decision.

- What type of force testing system does your application require (e.g., portable handheld force gauge or force gauge with stationary force test stand or universal testing machine)?
- What type of force need to be measured (e.g., compression, tension, torque, peel strength, flexure / bend strength, etc.)?
- What is the anticipated minimum and maximum force to be measured (e.g., force measuring range of 0 ... 500 N)?
- What degree of accuracy is necessary for the successful completion of your force testing task?
- What memory size and data transfer interface is needed, if any?
- What level of after-sales service and support is desired?
- What is your budget?

Following is a more detailed analysis of criteria to keep in mind when selecting a force gauge.

The answer to this question largely depends on the intended application. If you want to use the force gauge to sporadically collect readings for quality assurance, a portable force testing device should be used. If you want a more precise and repeatable force test, it will be better to use a stationary force test stand with your force gauge. In addition to providing stability, a stationary force test stand, also called a universal testing machine (UTM), can be equipped with an RS-232 interface or USB port, allowing the test stand to be controlled by a computer.

When selecting a force gauge, one must consider how the force is initiated. Tension is the pulling force, whereas compression is the pushing force. Both tension and compression are common forces measured by a force gauge. When testing peel strength, the force is initiated by adhesion. Flexure / bend strength is a test performed primarily on coatings to assess formability, ductility and elongation. Another common force measurement is torque. Torque is the force initiated by rotation. For torque measuring instruments, visit torque meters / torque testers.

For safety reasons, you must choose a force gauge that accommodates the maximum force to be measured. Then, a buffer should possibly be taken into account, if the required measuring accuracy permits it. In addition, hazards that may arise during the force measurement should be determined and eliminated accordingly beforehand. For example, if during a tensile force measurement, there is a risk that the test material could get twisted, the force measuring device must be secured by means of a clamp to prevent injury.

For applications requiring minimal force, a simple and cost-effective force measuring device is a spring scale. A spring scale measures weight or force, typically in grams (g), kilograms (kg), pounds (lbs) and / or Newtons (N), when an object is hung from the hook of the scale. Also called a spring balance, this mechanical force measuring device is ideal for physics force experiments and for teaching action-reaction in science, technology, engineering and math (STEM) classrooms and other educational settings. During measurement, the spring installed in the scale is extended or pulled. When released, the spring returns to its original state.

Another force measuring device with a mechanical measuring principle is a hydraulic force gauge. A hydraulic force gauge uses a hydraulic liquid to measure acting forces. Hydraulic force sensors are designed for much larger force measuring ranges in comparison to spring scales. However, the disadvantages of hydraulic force gauge devices are lower measuring accuracy, lower measuring resolution and lack of measurement traceability. For these reasons, digital force gauge devices are predominantly used.

A digital force gauge consists of two important components: the sensor and the meter or evaluation unit. In digital force gauge devices with lower measuring ranges, the sensor is often installed internally. For larger measuring ranges, the sensor is connected externally to the meter. Many digital force gauge products are multi-purpose and will measure both tension and compression forces, among other parameters such as rotation speed and triaxle vibration. There is no one sensor that could be suitable for all measurement tasks. Thus, these multi-purpose digital force gauge devices will often come with adapters and / or be programmed to perform mathematical measurement conversions.

An important parameter for a digital force gauge is the maximum possible sampling rate. Sampling rate is the frequency with which the transmitter checks the force sensor. It is often indicated as an Hz number. 1000 Hz means that the force sensor is queried 1000 times per second by the transmitter, and the transmitter is able to change the measurement data 1000 times per second. Low cost force gauges have only one sampling rate of 2 Hz which is sufficient for a slow force measurement but is definitely unsuitable for a tear test. Because of the slow reaction, many measurement data of the force influence during the tear test are lost and that is why are not meaningful.

The user is not able to process an enormous amount of data (1 kHz = 1000 Hz = 1000 values per second) during the measurement. So, here it also must be considered whether the evaluation system / transmitter is able to provide the user in any form with 1000 values. Thus, the measurement data can subsequently be evaluated individually. Some low cost transmitters of the force measurement can query the sensor, e.g. 1000 times, but are not able to provide the user with the data sufficiently and in the fullness, since the processing electronics is unable to process the measurement data at that speed. Then, the average values are calculated which are then passed further.

Another popular, albeit expensive, force measuring tool is a highly flexible resistance strain gauge (DMS). A DMIS is a thin film to which a wire pattern or measurement grid is adhered. This wire is supplied by an external voltage and changes the resistance or conductivity due to expansions and compressions. This change is so far proportional and reproducible that an external evaluation indicator can carry out the calculations of the force. These DMS films are then attached (glued) to the measuring points where the deformation can be recorded with the help of the measuring grid. However, it must still be taken into account that there are other influencing factors such as temperature, humidity, magnetic fields, etc., that can affect the conductivity and thus distort the readings. Just as in the finished force sensors the DMS films are easily placed at those places of the construction where the force exerts the greatest deformation. However, it must, by all means, be considered, that the DMS strips must have a fixed connection to the ground so that to give the deformation further. Thus DMS strips cannot be used again after they have been glued once.

The higher the maximum load of the sensor, the lower the measuring accuracy of the sensor. Thus, a compromise should be reached here. Each force gauge will have its own accuracy specifications that are dependent upon the range being measured. Typically a higher accuracy measuring instrument will come with a higher price tag, so it is important to consider practicality as well as precision.

Whether for a long-term or for a short-term measurement, in both cases, the data analysis is elementary. The data can be processed due to the special functions of the evaluation system / transmitter and provided to the user. If the user wants to determine, e.g., only the maximum force, the transmitter can present the highest value in the form of PEAK or MAX from the collected data (note sampling rate) and filter out the other readings. If the user still wants to determine the other reading such as, e.g., the average value, then possibly another function and filters are necessary. In the best case, the whole collected measurement values after the force test can be stored. These raw files allow even later to determine the desired results from the already carried out measurement experiments. So there is an evaluation system / transmitter from the force measurement which stores the measurement data in the internal memory and can provide the data to the user after the measurement. Another way to save the measured data is to transfer the data to a storage device such as a PC or data logger using an RS-232, USB, 4-20 mA or 0-10 V interface.

This is another important point to keep in mind. Find out how long the supplier has been in business. The longer the company's tenure, the more likely it is that you will be able to order spare parts a few years down the road after buying your force gauge. PCE Instruments has been in business since 1999. (For more details, please visit the About Us / Corporate History section of our website.) Also find out what kind of technical support will be available to you. Call PCE Instruments, talk to the technical support team prior to purchasing and see for yourself the level of service provided.

Often more is involved in the budget than just the cost of the force gauge. Calibration costs are common expenses that can occur when using a force gauge. For instance, if you need to meet the requirements of an ISO quality standard, a regular calibration interval needs to be adhered to. ISO calibration costs can occur at the time of purchase and reoccur on an annual or even semi-annual basis, depending on your accuracy needs and usage of the force gauge. It is also possible that recalibration becomes necessary later on, due to the drift that sensors can experience over time. Consumables like (rechargeable) batteries should be included in your calculations as well.

For robust weighing equipment, please visit the crane scales and heavy-duty scales sections of the PCE Instruments website.

Generally speaking a Force Gauge is a device used to measure the applied compression or stretching force (push / pull) or to define the moment of force (torque). Depending on the type such device allows to detect the force in the range from hundredth of kN to MN.

There are mainly two kinds: mechanical and digital ones.

A resilient element in the mechanical is a spring or lever. The force influences the spring and the latter is either compressing or stretching. The lever gauge is less accurate, the lever is deformed as a result of the force application. The weak point of the mechanical gauges is their dependence on the temperature and the inaccurate reading by the human eye.
In their turn, the mechanical devices can be of three kinds: Force gauges for general purpose – devices for measurement of the stretching force of class I and II, meant for operation in the rooms from -5° to +35° (II class) and from – 5° to +45° (I class) and relative humidity not more than 80%. Another kind is waterproof, which means the device can operate at relative humidity not more than 98 %. The third kind of compression and stretching Force Gauge is sample-like – meant for calibration of the measuring means at the laboratory.

An electronic force gauge is widely used in the automotive industry and transport, in the production of the automated technological systems or for mechanisms verification. The main element in the electrical force gauge is a strain gauge transducer which is used as a resilient element, measuring unit with the indicator and the connection cable. Different kinds of sensors can be used in the electrical gauges which widens the sphere of their application. These force measurement devices give much more accurate results, as there is also a cable allowing to transmit the data to the computer and process it digitally. The electronic devices transform the deformation of the resilient element into the electrical signal. For example, these devices are used to measure the force of compression of the automatic doors in the transport, garage, gate …

In medicine the portable, handheld device is necessary to measure the muscle force of the hands. It is often used in the medical and sport institutions, sanatoriums etc. There are special devices for children, as children muscle force which is different in the housing shape and size. These force gauges allow to make conclusions about the general physical shape of the patient. It is absolutely necessary on the rehabilitation stage as it helps to control how the body is developing after trauma. Compression model is required to measure the static compression force during the inspection test benches and machines.

Another application field is gas and oil production. Such devices can give signal about emergency loads, generate and print reports and test instruments. The duration of tests is shown on their displays with an accuracy of second.

A Force Gauge is often used to measure the tensile force of ropes during the test of the seal strength of anchors when fixing braces in the process of installation and repair of drilling rigs systems.

For the laboratory experiments and tests of new equipment the electronic models with the microprocessor control are used. These force gauges can be mounted on test stands.

A Force Gauge finds its application there where it is difficult to imagine it could be used, for example, there is a special Egg Force Reader a device which helps to measure the level of force necessary to break a shell of an egg. When using that device it is possible to find out the best ways of transportation and marketability of the product.

A Force Gauge is very often used for testing how string the floor is. This can be really an important issue at the factories or industrial rooms where it goes about heavy loads. A wide range of tests can be carried out in the process of production with the help of this device. Depending on the component parts of the force gauge different kinds of that device can be used in the testing, construction, production of goods, engineering, factories etc.

Also the Force Gauge is used in the chemical and textile industry. This device is priceless when it goes about checking how strong the fabric or fragile the material is. One of the important branches in animal breeding is down production. To make the production profitable it is necessary to guarantee the good quality product, which means, appropriate length, softness, strength, weight etc and etc. Force Gauge is applied to check the strength of the down.

In reality there can be dozens of examples when the force test instrument is applied, including automotive, medical, packaging, production areas.

Force gauge for testing wires and ropes
Wires are long thin metallic rods with a constant mostly round cross-section, while ropes consist of several natural or synthetic fibre cords or wires twisted together. Wires and ropes perform important load-bearing or transmission functions in many areas. There are areas of application with the rigid wires or ropes as well as with the wires or ropes that move according to the plan. Whether on high-voltage lines or overhead railway lines, on buildings, bridges, cable cars, lifts, cranes or other machines, tests before and after installation are intended to ensure that wires and ropes can fulfil their functions safely. New ropes are tested before the installation with a tensile testing machine or with a suitable force gauge in special fixtures. ISO 2307:2019 and EN ISO 2307:2019 and based on it DIN EN ISO 2307: 2019-12 "Fibre ropes – Determination of some physical and mechanical properties" specify, among other things, the methods for measuring the breaking force and elongation of the rope under tensile stress.

For tensile force measurements on the tensioned wires or ropes, a mobile force gauge specially designed for the rope force measurement can be used, which is set up so that the rope is guided on three rollers of the gauge. These special rope tension meters are available for different force ranges, rope diameters and with different lengths of the measuring distance. However, free access and sufficient space for mounting the measuring device are always required. If space is limited, the force gauge with a ring-shaped force transducer or a rope clamp can be used. These are also suitable for continuous monitoring of the forces on the installed rope.

Force gauge for testing spring forces
Technical springs are elastic components that deform under load and return to their original shape when the load is removed. The best-known forms include tension, compression and torsion springs formed from spiral spring wire, but also flat springs and spring clips. Springs are used for a wide variety of applications. The dimensions, shape and load capacity of the spring can be precisely adapted to the requirements of the application.

With a force gauge for testing spring forces, it is possible on the one hand to determine what force is necessary to achieve an intended deformation of the spring. On the other hand, a suitable force gauge can also be used to determine the range in which the deformation changes proportionally to the applied force. Within this range, the springs themselves can also be used to measure forces. With the spring constant or spring hardness determined from force and travel, the applied force can be calculated for each deformation of the spring or displayed on a suitable scale.

Often, the force gauge for measuring spring forces is integrated into a fixture that can be used to ensure the repeatable test conditions. Some of these load test stands also allow load cycle endurance tests on safety-relevant springs, the failure of which would have significant consequences. Whether on machinery, vehicles or equipment, correctly dimensioned and long-lasting springs are a prerequisite for smooth functioning or easy operation in many places, e.g. pressure switches, pedals and seat belts.

Force gauge for "peeling tests”
The term “peeling” stands for the flat peeling off of thin layers. In a peel test, the force gauge is used to test under specified conditions how much force is required to remove a film or other thin covering layer from the substrate. There are different methods, but the prerequisite for the peel test is always that the cover material reacts sufficiently flexibly to bending and can be lifted off as a layer.

In the case of the peel tests on packaging, it is often a question of ensuring that the packaging, e.g. for perishable foodstuffs, medicines and sterilised medical products, is tightly sealed but can also be opened again with a reasonable amount of effort. In the case of durable materials, on the other hand, the top layers should adhere as permanently as possible to the substrate, e.g. on floor coverings, doors or furniture. With some safety and protective films or adhesive tapes, it is also important that they can be easily removed from the substrate without leaving any residue, despite good adhesion.

Many composite materials, but also the adhesion of lids on the food packaging such as yoghurt cups, are tested by fixing the sample and lifting the top layer at an angle of 90 degrees, 180 degrees or 45 degrees to the substrate. In contrast, the adhesive strength of two thin superimposed layers, such as in the stretch films or pressed, welded or glued seals, is determined in the so-called T-peel test. In this T-peel test, the two films are pulled evenly in opposite directions. The force gauge suitable for the peel test can usually be clamped into the force measuring stands or fixtures where it is guaranteed that the speed and the direction of pull are maintained. In most test cases, the force gauge should not only display the maximum force, but also the force progression over the duration of the test. In the case of the product tests, this can also be used to determine the uniformity of the bonding and sealing.

Pedal Force Measurement
Just as per pedes means on foot, a pedal is a lever moved with the foot. Pedals are often used to operate certain functions on devices, machines, vehicles or musical instruments with the feet. The force applied to the pedal with the foot can be transmitted directly or after amplification or attenuation. Here, very different effects can be triggered with the pedals. In the motor vehicles, for example, separate pedals are used for accelerating, clutching and braking. On the machines, the pedals can also be used as safety or trigger switches. The force exerted by the operator's foot on the pedal to change the position of the pedal is called the pedal force. The forces required to achieve the desired effect can be determined with a pedal force gauge. If the specified values are not met, the pedal must be readjusted or replaced.

In the German guideline for testing the brake systems of vehicles during main inspections (HU) according to § 29 StVZO from 24 May 2012, the values for the minimum braking and the maximum permissible actuating forces for this are specified for various vehicle types. For passenger cars and motor homes weighing less than 3.5 tonnes, a maximum of 50 kilograms (or decanewtons) of force applied to the brake pedal should result in the desired braking deceleration. For buses, trucks, tractors and motor homes weighing more than 3.5 tonnes, the maximum force should be 70 kilograms (or decanewtons). Since the safety of the machines and vehicles should not depend on the physical strength of the user, the pedals are nowadays designed in such a way or their action is reinforced so that no great force is required to operate them. This is ensured by the brake boosters or the pneumatic brake systems. Appendix 2 of the HU Brake Directive describes a procedure that also uses the pedal force gauges to check hydraulic brake systems. In other European countries it is already compulsory to also determine the pedal force during the mandatory brake inspection. In Austria, for example, the inspectors have had to measure the pedal force required for the maximum achievable braking effect on the wheel since January 2020. The measured value must then be compared with the manufacturer's reference values.

Force measuring device for testing door and gate forces
Despite well-known negative examples and updates of accident prevention regulations, there are still accidents with personal injury at inadequately secured doors and gates. This mainly concerns power-operated doors and gates, including revolving doors, swing doors and gates, sliding doors and gates, as well as all types of vertically closing gates such as overhead, sectional and rolling gates.

The closing forces must be limited for all power-operated doors and gates that are not fully secured by dead man's controls, safety edges attached to the closing edge or contactless protective devices such as light barriers. This is checked by the trained experts with the suitable force measuring device. DIN EN 16005 and DIN EN 12453 define the measuring conditions and the limits for the level of the static and dynamic forces and their duration of action. The force measuring device used for testing the closing forces must therefore not only be able to record the maximum height but also the temporal course of the acting force.

The requirements for the force gauge specified in DIN EN 18650 Part 1 Paragraph 6.2.2 include:

- The force must be applied via a round measuring surface with a stiffness of 500 N/mm².
- The measuring frequency must be at least 200 Hertz over 5 seconds.
- It must be possible to measure forces from 25 N to 2,000 N.
- The measuring accuracy must be at least ±5 percent in relation to the measuring range.

In addition to safety, the operability of the doors in everyday use plays an important role. Modern doors that meet special requirements for sound, heat and fire protection should be easy to open and close despite these functions. Particularly in the case of buildings for the public and those intended for a user group with physical limitations, care must be taken to ensure that the operating forces of the doors also comply with the standards for the barrier-free buildings.