Measuring Current: Innovations in Electronic Meters, 1948-1970

Multimeter developed by Swail, c.1948

Throughout his career, James C. Swail sought to build devices that people who were blind or partially sighted could use to gain the experience and technical expertise needed to become employed within the fields of science and technology.[1] One of the first assistive devices Swail began working on when he joined the NRC was accessible electronic meters intended to test and measure current and resistance from a variety of electrical devices. He completed his first prototype of such a device in 1948, describing it as “a vacuum-tube voltmeter, which used a mechanical chopper, amplifier and headset as its auditory detector.”[2]

Swail Ammeter, c.1970

Swail’s approach to construction shifted in 1964 – rather than build meters from scratch, he began modifying existing devices.  One example of this new design is pictured here – an ammeter first manufactured by the company Bach-Simpson c.1970. This device is similarly made of grey-painted metal, but is rectangular in shape with rounded edges. Two round black dials with pointers are positioned side by side on a metallic metal plate at the front of the device. Like the first prototype, each dial is designed to point to a series of dots indented in the metal plate, representing a calibrated linear scale of voltage levels that are divided into ten main divisions and subsequent subdivisions.  This scale corresponds to different settings that can be adjusted by turning black knobs at the back and top of the machine. The knob at the top, intended to adjust voltage or resistance settings, is placed next to a white and black visual display, encased in a small black plastic frame. A round, metal-plated speaker is placed at the left-hand side of the apparatus, through which an operator can hear the voltage being read by the meter. Alternatively, a jack for plugging in earphones is placed at the back of the device, below a pair of matching vents.[4]