Compression test

Compression test Sinks The Compression test sink can be used to perform a dynamic compression test on a combustion engine. This quick and easy test gives a good impression if an engine has a compression problem or not without having to apply pressure sensors to the cylinders.

The starter current is measured during cranking and then used to calculate the relative compression of each cylinder. When the deviation of one or more cylinders is too big, this is indicated with a red bar. The Compression test sink uses a special output window, with a bar graph for each cylinder, as can be seen below.

Dynamic compression test during cranking of an engine with a leak in one of its cylinders Dynamic compression test during cranking of an engine with a leak in one of its cylinders.

Usage

The engine must be prepared such that it will not start during cranking. For a petrol engine for example, the ignition can be disconnected. Using a Current clamp TP-CC600 the starter current is measured. The oscilloscope must be setup to capture approximately 5 seconds of data at a sampling rate of 10 kS/s. The input range must be set to a value that can measure the high starter inrush current. Triggering must occur on the rising edge of the current peak, trigger time out must be set to infinite. The engine must then be cranked for 3 to 4 seconds.

Properties and actions

To control the behavior of the Compression test sink, several properties and actions are available. These can be accessed through a popup menu which is shown when the sink is right clicked in the object tree.

Cylinder count

The property Cylinder count tells the sink how many cylinders the engine has. It must be set before perfomring the measurement. It can be set to any value from 2 to 24. The default value is 4.

Bring to front

When the Compression test output window is hidden behind another window in the Multi Channel software, the action Bring to font will make it visible. The Bring to front action is available in the popup menu.

Common properties and actions

Alias

You can change the displayed name of an object by giving it an Alias. This can be handy when you are dealing with a lot of objects and have problems keeping them apart. You can for example give channel one of your instrument the alias "Battery", when it is measuring a battery voltage. To give an object an alias, use the item Alias ... in its menu. To remove an alias and revert to the original name of the object, set the alias to an empty string.

Disconnect all sources

To disconnect all sources from an I/O or Sink at once, use the Disconnect all sources action.

Clone

When a new object is to be created, similar to an already existing object, with the same properties, the Clone action can be used. This will create an identical copy of the original object, with the exact same properties. Source(s) and sink(s) of the new object are not yet connected.

Delete

The Delete action deletes a source, I/O or sink. All connections of the object will be disconnected and then the object will be removed from the object tree. The source property of the objects that used this object as source will be cleared. The sink property of the objects that used this object as sink will be cleared. An axis in a graph that was connected to this object will be also deleted.

Load

The Load action allows to load the settings and data for an object from a TPS or TPO file. This is detailed described on the page about Loading into selected objects.

Save as

The Save as action allows to save the settings and data of one or more objects to a TPO file. When multiple objects are selected, the connections between the objects are saved as well. This is detailed described on the page about Saving objects to a TPO file.