RM History


A research project in 1961 led to the first fully automatic electronic microbalance design, subsequently to be perfected by CI Electronics Ltd. In this innovative design, a “closed loop servo system” was established using an optical detector attached to the beam which via an amplifier continually adjusted the current level in the coil causing it to maintain the beam in its equilibrium position. Changes in the current were accurately proportional to the weight of the suspended sample. Digital displays were becoming available at the end of that decade so that the weight could be displayed continuously and it could be recorded and printed out repetitively in synchronism with time and any of the other parameters being monitored.

Until the 1950s only mechanical balances were commercially available and the visual operation to record data was slow, cumbersome and unsuitable for applications where small samples and higher precision were needed. The advantage of using small samples (eg 1 gram or less), where data to microgram precision was needed, was lost if only a precision laboratory microbalance was available, not least due to the skill and patience required for its use.

One alternative suitable for some applications comprised a helical quartz spring having a vertical axis and from which the sample was suspended. While awkward to set up, it had the unique advantage that being only made of quartz, with a small mirror attached, it could operate in virtually any environment without being damaged or becoming inaccurate. An optical system comprising a beam of light reflected by the mirror was directed on to a scale. It was difficult to calibrate, or provide absolute sample weight data, but with care it could be used to record the very small weight changes which are often of more experimental significance.

The picture changed dramatically in the 1960s when the electronic microbalance appeared. It comprised a miniature beam from one end of which the sample was suspended. Deflection of the beam was counteracted by a current in a coil attached to it which was positioned in the field of a permanent magnet. This used the Faraday effect, (dating from 1831), whereby the current in the coil is directly proportional to the torque applied to the beam. To operate the early microbalances, which used this principle, it was necessary to adjust a calibrated potentiometer to provide a current which set the beam to a null position.

Today CI microbalances are renowned for their robustness and accuracy. Many are still in use after 25 years or more of operation.

CI microbalances have long been, and still are, the balance of choice for many manufacturers of gravimetric instruments, particularly noted for their high load capacity (ability to hold weights of up to 5g) and their wide dynamic range of +/-500mg, resistance to corrosion due to the gold plating of the balance arms and PTFE coating option.

Versions of the MK2 balance in Stanton Redcroft thermogravimetric instruments, VTI water sorption analysers and HighTemperature High pressure TGA systems and instruments for Hiden Analytical.

CI continues to invest in improvements to the balance performance, new test facilities and improved electronics control.