# 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](https://docs.irs.systems/ltt/documentation/ltt-gui-manual/teststand/limittests/standardlimittests):

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

The LTT software adds a fourth type of limit test - the [LTT limit test](https://docs.irs.systems/ltt/documentation/ltt-gui-manual/teststand/limittests/lttlimittests). The LTT limit test is a combination of the numeric and string limit tests and allows limits to be [configured by XML file](https://docs.irs.systems/ltt/documentation/ltt-gui-manual/configuration/generatedfiles/limitsconfiguration). 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](https://1704635928-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FH5etzy4TvPRLxLRNfHlb%2Fuploads%2Fgit-blob-584eb1383cc1349673b2d747c03397d8da09a8a4%2FLTT_Limit_Test_Dialog.png?alt=media)