typically very expensive pieces of equipment, and so are normally used only in certain fields that rely on them for a particular purpose. Types of dynamometer systems A 'brake' dynamometer applies variable load on the prime mover (PM) and measures the PM's ability to move or hold the RPM as related to the "braking force" applied. It is usually connected to a computer that records applied braking torque and calculates engine power output based on information from a "load cell" or "strain gauge" and a speed sensor. An 'inertia' dynamometer provides a fixed inertial mass load, calculates the power required to accelerate that fixed and known mass, and uses a computer to record RPM and acceleration rate to calculate torque. The engine is generally tested from somewhat above idle to its maximum RPM and the output is measured and plotted on a graph. A 'motoring' dynamometer provides the features of a brake dyno system, but in addition, can "power" (usually with an AC or DC motor) the PM and allow testing of very small power outputs (for example, duplicating speeds and loads that are experienced when operating a vehicle traveling downhill or during on/off throttle operations). Types of dynamometer test procedures There are essentially 3 types of dynamometer test procedures: Steady state: where the engine is held at a specified RPM (or series of usually sequential RPMs) for a desired amount of time by the variable brake loading as provided by the PAU (power absorber unit). These are performed with brake dynamometers. Sweep test: the engine is tested under a load (i.e. inertia or brake loading), but allowed to "sweep" up in RPM, in a continuous fashion, from a specified lower "starting" RPM to a specified "end" RPM. These tests can be done with inertia or brake dynamometers. Transient test: usually done with AC or DC dynamometers, the engine power and speed are varied throughout the test cycle. Different test cycles are used in different jurisdictions. Chassis test cycles include the US light-duty UDDS, HWFET, US06, SC03, ECE, EUDC, and CD34, while engine test cycles include ETC, HDDTC, HDGTC, WHTC, WHSC, and ED12. Types of sweep tests Inertia sweep: an inertia dyno system provides a fixed inertial mass flywheel and computes the power required to accelerate the flywheel (the load) from the starting to the ending RPM. The actual rotational mass of the engine (or engine and vehicle in the