# Limit Tests

The purpose of a LTT testplan is to test DUT outputs (signals) against certain limits. Hence, the limit test is the most important TestStand concept for LTT.

TestStand offers 3 [standard limit test types](/ltt/documentation/ltt-gui-manual/teststand/limittests/standardlimittests.md):

* numeric limit test
* string limit test
* pass/fail test

The LTT software adds a fourth type of limit test - the [LTT limit test](/ltt/documentation/ltt-gui-manual/teststand/limittests/lttlimittests.md). The LTT limit test is a combination of the numeric and string limit tests and allows limits to be [configured by XML file](/ltt/documentation/ltt-gui-manual/configuration/generatedfiles/limitsconfiguration.md). That way it is easily possible to change limits without changing the the testplan itself. Additionally the LTT limit test step provides a **limit selection panel** in TestStand, where you can easily **select the signal and limit** you want to test.

![LTT Limit Test Dialog](/files/RaDq21FpUT4anPGw9gKF)


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