Frequently asked questions about QTC
Can QTC be transparent?
QTC is a composite comprising an elastomer with filler particles. Although transparent elasTomers are readily available the filler is opaque and this predominates. QTC is therefore never transparent.
Are there different types/sensitivities of QTC?
Yes, and Peratech selects the desired properties of the QTC used for each component product. For instance the QTC Pills and QTC Ink Coating use very different QTCs. It is also possible to use the applied voltage, mechanical coupling, and thickness of material to tune the sensitivity of QTC in any particular application.
What force is required to produce a resistance change?
This varies across the products. The force levels normally operated within are from about 60N down to 0.1N. These are the terminal load forces required to take the QTC to below 10 ohms resistance (for Pills).
Is QTC is a good sensing material?
QTC makes an ideal dynamic force or pressure sensor. In order to use QTC to measure static forces the correct formulation and design is required. Similarly compensation for factors such as temperature and other external factors may be required. QTC is not designed to replace strain gauges in weighing applications.
Is QTC immune to humidity?
Yes. QTC is immune to humidity and can also be used as an encapsulant for the electrode structure
Is QTC immune to electrical interference?
As an element within a circuit QTC is only as prone to interference in the same way as the rest of the circuit will be.
Within what tolerance can QTC be manufactured in volume?
Variance to load pressures in the bulk material will be more to do with external conditions than with the absolute repeatability of the QTC material, which is good but has a non-linear response. If the practical range of resistance is considered to be one billion ohms, then a repeatable processing tolerance can be shown which in terms of Resistance v Force equates to better than one percent.
Is QTC expensive?
Peratech price QTC components very competitively for volume applications. QTC can compete successfully in cost competitive industries such as switching, automotive, toys and textiles
Can QTC be easily processed?
In general most standard processes can be used with QTC. It can be extruded, moulded, coated and calendered. Machining depends on the precise form of the QTC and the process.
Can QTC be easily integrated?
Electrically QTC works just like a variable resistor so integration is simple. Mechanical integration is usually also simple however placement and application of contact electrodes can be critical to correct operation.
Can QTCs have a degree of unstrained conductivity?
Yes, a 'start resistance' can be obtained by using shrinking binders and/or additional fillers.
Is QTC safe?
In general QTC is very inert. For full details please consult the MSDS for the product concerned. QTC has passed BS EN 1811:1999; the reference test method for release of nickel from products intended to come into direct and prolonged contact with the skin.
How much does resistance change with temperature?
This depends on the QTC used. For a QTC Pill for a current of 1microA an approximately linear increase in the resistance (R=63MOhm to R=1240MOhm) is observed over a temperature range 25°C to 180°C.
Does QTC work at mains voltage?
The maximum specified voltage for QTC components is 40V, however it is possible to use QTC elements in series to achieve control at higher voltages.