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The VFC-2, VFC-2b, VFC-2e, and VFC-2n printed circuit boards (PCBs) are used to implement several variations of an AD537 based voltage to frequency converter (VFC) for use in
temperature tools; schematics
VFC2a.sch,
VFC2b.sch,
VFC2d.sch,
VFC2e.sch, and
VFC2n.sch show various versions. These boards were primarily designed for upgrades / remanufacturing of older temperature tools and perform well to 350° F (175° C), but are useable to 400° F (200° C). A
platinum RTD sensor is used with these circuits, and the inherent high gain of the AD537 makes an elegant low parts count solution possible. The industry standard "ten counts per degree" scheme is used by default, but other scaling is easily implemented. The "Zero" (offset) and "Span" (gain or scaling) trimpots operate independently with absolutely no interaction; calibration is a breeze. There is a provision for adding either positive or negative temperature coefficient correction if required (not present on VFC-2e). A ten (10) volt power supply is usually used, and power consumption is less than five (5) milliamps (our
106LVPS-3 is a good power supply candidate). The single semiconductor is ordinarily mounted in a high quality machine pin socket, but can be mounted directly to a VFC-2 PCB if low clearance is required. All boards are jumper configurable to be compatible with either armor / chassis negative or armor / chassis positive line power. The VFC-2, VFC-2b, and VFC-2e PCBs are 0.8 inches wide and mount on two (2) inch centers; the VFC-2n PCB is designed for one inch temperature tools and is only 0.6 inches wide and mounts on two (2) inch centers.
The VFC-2, VFC-2b, VFC-2e, and VFC-2n PCBs can be used to upgrade tools, or they can be used in new tool construction. Just add a power supply board, and a pulse former / line driver board, and voila, instant temperature tool! These boards use readily obtainable components, which parts will continue to be available for many years to come, and they use convenient turret terminals for wiring connections. We prefer through-hole components for PCBs designed to survive high temperature, but selected components may be surface mount (SMT), or have provisions for either through-hole or SMT where price and/or availability is an issue. Due to time constraints on maintaining this website, the PCB illustrated below may not be the most recent revision of the board and / or circuit.
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