MULTIPLE UNTWIST-TWIST METHOD:-

Multiple untwist-twist method:-

The straight forward untwist-twist method is subject to a variable error owing to the fact that , the number of turns to return the yarn to its original length as not , the same as the number of turns to take the twist out. This is mainly because when the yran is spun some of the distartion becomes permanently set into the fibers so that when the twist is removed the yarn is not ad straight as it should be . This is particularly a problem in the yarn made from wool fibers , especially those that have been deliberately treated in order to set the twist.

Fig. The multiple twist-untwist method.

The multiple untwist-twist method aims to overcome these problems by repeating the untwisting and twisting action which causes the errors due to the source to be progressively reduced. In the test shown diagrammetically in Fig. , The yarn is untwisted and retwisted because to its original length as in the normal test and the number turns A noted. The value A contains an unknown error without the counter being zeroed, the direction of turning is reversed and the yarn untwisted and twisted back to its original length. This ought to bring the yarn back to its original condition, however owing to the error d 1 and d 2. By untwisting and retwisting a third time further ready C is obtained which contains the error rf 1d 2 and d 3 shown in figure. Combing the trading A, B and C give, 

A-2 BH-C=4X

Where X is the number of turns in the length of yarn tested.

The method relies on the error d 1, d 2, and d 3 becoming progressively smaller so that the remaining error in the above equation is the difference between d 2 and d 3 can be ignored. It is possible to carry on futher untwisting and twisting in the same manner to reduce the error even further.

Automatic twist tester:-

An automatic twist tester is produced (Z Weigle D 302);which takes the tedium out of the large number f test required for determining twist. The necessarily depends on untwist-twist type method for determining twist levels and cannot detect fiber straightened  automatically.

image of an automatic twist tester machine ref by India Mart.

Take up Twist tester:-

Take-up is the Different between the twisted and untwisted length of yarn twist tester are available with moveable non-rotating jaw, which slide away from the rotating jaw to take up the slack as twist removed . This allow the length of difference to measured.

Ref:-https://textileapex.blogspit.com