Vishay has unveiled two series of Bulk Metal Foil high-precision Accutrim trimming potentiometers. The potentiometers are designed to meet and exceed the requirements of MIL-PRF-39035 Char. H. The 1/4inch2 RJ26-style 1240 series and the 3/8inch2 RJ24-style 1260 series offer low end-to-end TCR of ±10ppm/°C from -55 to +150°C. They feature +25°C reference and ±25ppm/°C through the wiper. Load life stability of the devices is typically 0.1% under full rated power at +85°C for 10,000 hours.
The two series of high-precision trimmers feature a Bulk Metal Foil resistive element that possesses inherent temperature and load life stability. The advanced, virtually backlash-free adjustment mechanism of the devices allows them to be set quickly and accurately. The adjustment mechanism of the devices maintains this setting through temperature cycling and vibration, as well as thermal and mechanical shock. Trimmer potentiometers are stable in vibration environment and eliminate the need for unwanted adjustments. The devices offer a multi-fingered metal wiper that engages a planar surface of etched Foil for low TCR end-to-end.
The trimmers feature 0.1% typical setting stability and a wide resistance range from 5 to 10kOhm. The devices feature standard resistance tolerances of ±5% and ±10%. The devices offer 0.25W power rating at +85°C and provide high ESD immunity. They can withstand electrostatic discharges of up to 25kV. The devices provide unidirectional, infinite resolution, which when synthesised by a combination of a uniform resistance material, multiple wiper contact points and multiple resistance circuit paths, yields setability of less than 0.05%. There are no turns of wire to be traversed and this causes a step function. There is no contact resistance variation to cause an irregular change in resistance with mechanical adjustment.
The 1260 devices offer tin/lead terminations, while the 1240 devices feature gold-plated terminations with tin/lead terminations on request. The trimmers provide an 'O'-ring to prevent ingress of fluids during any board cleaning operation. They are available with special options including special markings, burn-in and screening operations. The stability and linearity of the foil trimmers eliminates the need for a buffering resistor in series with the trimmer or a linearising resistor in parallel with the trimmer. The low values available in foil trimmers are linear and make the devices suitable for end to wiper circuit use.
