An Integrating and Differentiating Bar‐Magnet Velocity Meter for Use in Ballistocardiography

An integrating and differentiating bar‐magnet velocity meter is described. Design criteria are presented for integrators and differentiators to meet given specifications of frequency response. In the design of the differentiator, use is made of a small amount of resonance magnification in a suitably damped series‐resonant circuit. Test procedures are described for determinations of frequency response, sensitivity, and linear range of the instrument. Examples are given of sensitivity adjustment and installation procedures for use of this instrument in ballistocardiography. A ``60 cps hum compensator'' is used to cancel out any objectionable 60‐cycle pickup from the power line.