Force Gage

If you wish to use your force gage to sporadically make measurements for quality control, a portable force gage will be the right choice. If a more accurate and repeatable force measurement is required, it is recommended to use a stationary force test stand with your force gage. A force test stand does not only provide stability but it can also be equipped with a USB or RS-232 interface so that it can be controlled via a computer.

For safety reasons, it is very important to choose a force gage that accommodates the maximum force you wish to measure. A buffer should also be taken into account if the required accuracy allows this. Also, possible risks must be eliminated before the force measurement. For instance, if there is a risk that the test material could get twisted during a tensile force measurement, the force gage must be secured with a clamp to prevent injury.

For measuring tasks requiring minimum force, spring scales can be used. These are easy to use and do not cost as much as many other force meters. Spring scales measure the weight and/or the force of an object that hangs down from its hook. The weight or force is normally measured in g, kg, lbs and / or N. A spring balance is a mechanical force tester that is ideal for force experiments in physics lessons as well as for showing the action and reaction in science, technology, engineering and math (STEM) classes and for lots of other educational applications. During a measurement, the spring is extended or pulled. When released, the spring returns to its original position.

A hydraulic force gage is another type of mechanical force measuring device and uses a hydraulic liquid to measure acting forces. The sensors of hydraulic force gages are designed for much wider measurement ranges than spring scales/balances. However, a hydraulic force gage will normally have a lower accuracy and resolution and little measurement traceability. This is why digital force gage models are more popular than analogue ones.

A digital force gage consists of a sensor and the evaluation unit. Most digital force gage models with lower measurement ranges are equipped with an internal sensor. Models with wider measurement ranges often come with a sensor that is connected to the gage externally. Most digital force gage devices measure both tensile and compressive forces and often some other parameters like the rotational speed or triaxle vibration. As not all parameters can be measured with a single sensor, most multi-purpose digital force gages are provided with adapters and some can do mathematical measurement conversions.

The maximum possible sampling rate is a very important factor when buying a digital force gage. The sampling rate is the frequency at which the transmitter checks the force sensor. It is normally indicated in Hz. For example, 500 Hz means that the force sensor is queried by the transmitter 500 times/s and the transmitter can change the measurement data 500 times/s. Lower-cost force gage models only have a sampling rate of 2 Hz. This sampling rate is fine for a slow force test but is not suitable for a tear test. Due to the long reaction time, a lot of measurement data would be lost during the tear test.

It must also be considered whether the transmitter is able to provide these many values in any acceptable form so that the measurement data can then be evaluated individually. Some low-cost transmitters can query the sensor, e. g. 1000 times per second but are not able to make the data available to the user in an appropriate way as the electronics are unable to process them at that speed. In that case, the average values are calculated.

The last type of force gage is rather high-priced but still very popular. It is called a highly flexible resistance strain gauge, commonly abbreviated as DMS which stands for the German word “Dehnungsmessstreifen”. A DMS is a thin film which a wire pattern or measurement grid is adhered to. This wire is powered by an external voltage and changes the conductivity or resistance in line with expansions and compressions. This change is repeatable and proportional so far that an external evaluation indicator can calculate the force. These DMS films are then attached (glued) to the measuring positions where the deformation can be recorded by means of the measuring grid. However, other influencing factors such as magnetic fields, temperature, humidity, etc., must be taken into account as these can affect the conductivity and thus manipulate the readings. Similar to force sensors, DMS films are placed where the force causes the most considerable deformation. However, the DMS strips must have a fixed connection to the ground and cannot be used again after they have been glued once.

The higher the maximum load of the sensor, the lower its accuracy will be. You will need to find the right compromise for your application. The accuracy specification of a force gage always depends on the range being measured. Logically, higher measuring precision will mean a higher price in most cases.

When it comes to the budget, not only the cost of the force gage itself must be taken into account. Regular calibration costs, for example, should also be considered. For example, if you must meet the requirements of an ISO quality standard, a regular calibration interval must be met. ISO calibration costs occur at the time the force gage is purchased and reoccur annually or even more frequently, depending on your requirements regarding the accuracy and the usage of your force gage. Recalibration may also become necessary later due to the sensor drift that can occur over time. Costs for consumables such as (rechargeable) batteries and for spare parts should not be neglected either.

Data analysis is an essential factor for both short-term and long-term measurements. Data can be processed due to special functions of the transmitter / evaluation system and made available to the user. For instance, if the user only wants to measure the maximum force, the transmitter can show the highest value from the collected data (quantity of data depends on sampling rate) in the form of a PEAK or MAX value and filter out the other readings. If the user wants to have other readings such as the average value, another function or filter will be necessary. Ideally, all values collected after the force measurement can be saved. These raw data even allow the user to determine the desired results from the measurements already made later. The evaluation system or transmitter saves the measurement data to the internal memory and can make the data available to the user after the measurement. There is also a different way of saving the measured data: you can also transfer them to a storage device such as a data logger or computer by using a USB, RS-232, 4 … 20 mA or 0 … 10 V interface.

It may also be a good idea to find out for how long the supplier has been operating. The longer the company has done business, the more likely it is that spare parts for your force gage will still be available to order a few years later. PCE Instruments was founded in 1999 and should be able to provide spare parts for all force gages that are still part of the company’s product range. You may also want to find out what kind of after-sales support will be available to you. You can call PCE Instruments to have a word with the technical advice team prior to purchasing to find out whether the level of service provided is sufficient for you.