Download RAW file: https://library.csbe-scgab.ca/docs/journal/3/3_1_2_raw.pdf
Considerable use is now being made of recording simultaneously the instantaneous values of draft or torque and ground speed to obtain more accurate estimates of the power requirements of farm implements in various field conditions. From these recordings or traces, average values are determined and the horsepower calculated. The tracing pens of these recorders may be actuated by mechanical, hydraulic, or electrical means. The electric pen motors or galvanometers, however, must have a high frequency response in order to follow the fast varying signal of draft or torque and tor this reason an oscillograph is required. In addition to draft and ground speed, this equipment can be used to measure pressure, vibration, velocity, acceleration, displacement, and such other phenomena as may be useful in research or evaluation. The devices to convert these physical properties into appropriate electrical signals are termed transducers.
the design and application of draft transducers using strain gauges
Harrison, H.P. and W.B. Reed 1961. THE DESIGN AND APPLICATION OF DRAFT TRANSDUCERS USING STRAIN GAUGES. Canadian Agricultural Engineering 3(1):2-29.