A force is an influence (such as a push, gravity, or friction) that causes an object either to change its velocity or to store energy through deformation.

The SI unit of force is the newton, symbol N - one newton is defined as the force required to accelerate a mass of one kilogram at a rate of one metre per second, per second.

The accurate measurement of force is vital in many areas, such as engine thrust determination, the weighing of large structures, and materials testing.

We have machines that can generate push (compression) and pull (tension) forces - these machines calibrate transducers that can then be used to make traceable force measurements.

If the acceleration due to gravity is known, the downward force generated by a weight of known mass can be calculated. This is the principle behind deadweight force standard machines - the mass values of their internal weights are adjusted so that, at a specific location, they generate particular forces. At NPL, gravitational acceleration is approximately 9.811 82 m·s^-2, so a steel weight with a mass of 101.933 2 kg will generate a downward force of approximately 1 kN when suspended in air.

Forces above 1.2 MN (the capacity of our largest deadweight machine) are generated hydraulically - oil at a known pressure pushes on a piston of known size to generate a known force. Our largest hydraulic machine can generate forces of up to 30 MN.

Research

Our main activity in the area of force is the dissemination of the unit of force to industrial customers. In order to do this, we need to maintain a range of force standard machines in good working order and periodically verify that the forces generated within them are within their specified uncertainty budgets. This involves comparisons both between pairs of machines at NPL and also between NPL machines and those at national measurement institutes in other countries.

We are currently developing a 5.04 MN build-up transducer – this is a force measurement system comprising nine 560 kN force measuring elements (each of which can be calibrated individually in our 1.2 MN machine) which will be used to improve the traceability of our 5 MN hydraulic force standard machine.

Products & Services

We provide a wide range of measurement services in the force area, ranging from the calibration ( PDF 116 KB) of all types of force transducer in our national force standard machines to the verification of industrial force testing and calibration machines. In addition, we calibrate strain cylinders ( PDF 191 KB) (used to verify concrete cube testing machines), DC ratio meters ( PDF 211 KB) (used as electrical instrumentation for force transducers), and extensometer calibration rigs ( PDF 181 KB).

We offer consultancy ( PDF 203 KB) in force measurement and are able to design and manufacture force calibration machines ( PDF 381 KB) for other laboratories. We also design, manufacture, and supply load cells ( PDF 209 KB) for specialist applications such as high accuracy, high force, and physically restricted working areas.

We provide a free technical advice service and would be happy to discuss any force measurement problems or applications with you.

Download flyer outlining Force measurement services available ( PDF 221 KB)

Collaboration

We operate a user group within EMAN (the Engineering Measurement Awareness Network) called the Force, Torque, and Hardness Special Interest Group.

The Weighing Panel of the Institute of Measurement and Control (InstMC) reports to the Learned Society Board of the Institute and was formed in 1990, with a remit of considering and promoting standards, codes of practices, and general understanding in all areas of industrial process weighing.

Contact

For more information about force, torque, hardness, and extensometry please contact: Andy Knott