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The
VFC-3 Voltage to Frequency Converter (VFC) printed circuit board (PCB) is a simple and reliable AD537 VFC integrated circuit-based low parts count VFC solution for
caliper tools. The design is a synthesis of an SIE caliper electronics section with our
VFC-2 temperature tool concept. The inherent high impedance of the AD537 makes an elegant low parts count solution possible, and the "Zero" (offset) and "Span" (gain or scaling) trimpots operate independently with no interaction. The VFC-3 allows unprecedented calibration adjustment and includes a linearization trimpot (30-35 kilohm is a good trial value for general use for trimpot VR-2 and resistor R2 combined, assuming a 10 kilohm linear transducer). Calibration schemes like 100 counts per inch, with 4 inches = 400 counts and 12 inches = 1200 counts, are easily implemented. Scaling resistor R4 and fixed linearization resistor R2 are turret terminal mounted for ease of selection or change on a fastened board. 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 the VFC-3 PCB if low clearance is required. The VFC-3 PCB is jumper configurable to be compatible with either armor / chassis negative or armor / chassis positive line power. The VFC-3 PCB measures 0.8 inches wide and mounts on two (2) inch centers. The 106VFC-3n PCB is designed for small diameter tools and is only 0.6 inches wide and mounts on 2.5 inch centers (see the
VFC-3n schematic and the
VFC-3 schematic for other minor differences between the VFC-3 and VFC-3n PCBs).
The VFC-3 PCB can be used to upgrade tools, or it can be used in new tool construction. This board uses readily obtainable components, which parts will continue to be available for many years to come, and it uses 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.
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