Digital dynamometer/indicator (DDI)
A 21st century approach to the investigation, analysis and improvement
model steam engine performance

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A unique tool for performance measurement and development of steam engine designs of all types
including traction engines, locomotives and stationary engines

First developed in conjunction with the Taylor Kellar partnership for use in our workshop, the original version of the DDI enabled us to record steam indicator diagrams from a running engine - in our case "Stafford", to see if the valve gear  we'd designed worked anything like the simulator predicted.

To improve portability, allowing live monitoring of an engine under test out on the road or track, a production version was developed housed in a robust enclosure, communicating with an Android device - either a smart phone or tablet - via a wireless Bluetooth link. A pair of strain gauges have been incorporated into the unit, allowing drawbar pull to be measured with speed, distance, work done and drawbar horsepower displayed - installed in a driving truck, the unit forms the basis of a fully functioned dynamometer, capable of storing several hours of data which can be downloaded to a PC for permanent storage and analysis. We took our own truck down to Bristol SME where we had an interesting morning running around coupled in tandem with their dynamometer car - there's a clip of it running here.

The standard device is supplied with an index sensor which, fitted to the wheel of either locomotive or driving truck, enables monitoring of speed and distance travelled. An in-built load cell records tractive effort throughout a run, providing a complete, compact dynamometer.

           An optional pressure sensor, connected to the cylinder of an engine under test (normally by removing a drain cock), adds comprehensive steam indicator functionality, with live display of the indicator diagram, mean effective pressure and indicated horsepower. In addition to assessing the power produced, the diagrams provide a powerful diagnostic tool for investigation of many problems, including:

The indicator has become an indispensible tool in our workshop, allowing the rapid evaluation and adjustment of all types of model steam engines, from 3 1/2 inch gauge locomotives to large scale traction engines. It provides a rapid method of diagnosing a wide range of problems and checking the performance of engines after servicing.

Customers to date range from leading locomotive designers/restorers to clubs wanting a  fast, reliable method of monitoring efficiency trials.



Dynamometer display, shown on Android tablet


Indicator display, shown on Android smartphone





88 x 110 x 48mm L x W x H




4 off M5 threaded holes, 20mm max intrusion fastener into case


Bluetooth link to smart phone or tablet running Android 2.2 or later

Index sensor

One supplied, Hall Effect with Neodymium magnet

Pressure sensor

1/4 x 40 tpi fitting, 0-25, 0-60 and 0-150psi ranges, user selectable

Drawbar sensor

Pair strain gauges with limit stops


0 40lbf (low) and 0 150lbf (high) ranges, user selectable

Data logging

6 hours storage sampling at 1Hz, last 30 seconds displayed on screen


TKP v1.5, free download from Android market


12 volt rechargeable pack giving 24 hours use


Recharge time 12 hours


Device can be recharged or run using charger

Charger 240 volt mains, 12V 0.5A output, 5.5/2.5 plug to device


Setup and operation instructions online


12 months return to manufacturer


January 2014 pricelist - including VAT at 20%

Standard unit c/w drawbar & index sensors for dynamometer use


As above, but including pressure sensor for indicator use 


Telephone 01526 328772
International +44 1526 328772

Copyright 2000-2014 Station Road Steam Ltd