A dynamometer car is a railroad maintenance of way car used for measuring various aspects of a locomotive's performance. Measurements include tractive effort (pulling force), power, top speed, etc.
Harry L. Dixon
From The Miniature Locomotive, July/August 1953
The photo shows you an interesting device that is being developed by Mr. William Brower of Berkeley, Calif.
A dynamometer car is to check the operation of a locomotive while in operation. This unit is still in construction and engineering stage, however, I felt that it has something of interest even at this time. A more complete story will be forthcoming along with detailed pictures.
Briefly, what you see is a flat car made from aluminum with the large set of wheels being one foot in circumference which are geared to the tape recording device in a ratio of 1:1.
The clamp looking unit in the foreground is fastened or installed between the locomotive and the riding car. On this connector is a silphan bellows and a spring that is calibrated for the scale of engine to be tested. The one shown is for 3/4 inch scale locomotive. As the load is applied to this spring the silphan bellows transfers pressure through the oil filled hose line to another silphan bellows, which operates the indicating needle mechanism. This affects a register on the tape that is moving in ratio to the speed you are traveling. The tapes will be calibrated to give you the draw-bar pull, the footage of track covered and the speed traveled during the test.
It is interesting to mention that the draw-bar pull will be recorded for all parts of the track covered, re: grades, etc.
It is to be expected that as the construction of this continues other engineering features may be developed and incorporated to make this dynamometer car very interesting to one who wants to see what his locomotive will do.