1. Transformation ratio: For transformers the transformation ratio is more  important  parameter than inductance.  You might be  testing only inductance values . With VLRTZ you can test   the transformation ratio and winding phase  in addition to inductance values.
 
2. Bifilar windings: Bifilar windings  are meant for perfect coupling. The only test for the bifilar winding is the transformation ratio and not  the inductance value. But you might be  testing  inductance  only and satisfying with it. By testing inductance you can not guarantee the bifilar winding. The only and the best test  is transformation ratio which assures the coupling.
 
3. Turns testing: The main  process of the transformer manufacturer is to wind the bobbin or coil.  Turns or TR test  is the main process test for winders. For  coils and transformers with closed cores; the  Inductance will not guarantee the turns. The closed cores can not give precise AL values. The inductance values must be given with a wide range. Presume that the core has +30% AL value and number of turns were accidentally put with -15%. With these conditions  the transformer is accepted without expected performance.  Once you define the core and number of turns, you have no control over the inductance value. Testing the number of turns of the bobbin is very  important. VLCTZ can be upgraded for turns testing apart from  other existing parameters by attaching TURNS TEST PLATFORM. Otherwise the transformation ratio test in addition to inductance value would guarantee the required transformer function.

4. Centre tap: Centre tapping is a regular requirement for the transformer manufacturers. Instead of taking the tapping at the time of winding;  it is a common practice to either  wind as a bifilar or wind  separately  and then join them in series. In a bobbin with multiple windings locating the start and finish may not be possible by visual checking. So you have to make some way of cross checking the start and finish of the windings to make the terminations properly. One way is to put the windings in series and check the inductance and thus locate the start finish and   terminate. The best way is to check the transformation ratio. When you are testing the transformation ratio with VLCRTZ  you are  locating the start finish and also cross checking the transformation ratio.

5. Test Conditions: To understand test conditions let us consider the following case. A  transformer manufacturer carefully tests and supplies to the buyer. The buyer rejects the  transformers saying that the inductance values are not within limits. The vendor tests them again in his instrument and finds the values well  with in the limits.  His instrument is showing correctly with some other coils. But where is the problem? There must be some scientific reason. The most possible reason could be in the specification itself. Some absent minded  engineer  designs and  closes the drawing ignoring some important specifications.

The value of an inductor depends more on the conditions of measurement. This is particularly true for iron core (ferrite also)  inductors for  which measurement repeatability with in a few percent is considered good and is usually adequate. Most of the higher value inductors are iron cored (ferrite or laminated cored). Iron core inductors are non linear and therefore the measured inductance depends on the level of the test signal, test frequency, measurement mode etc. Inductance value  without giving the test conditions is incomplete specification. Many designers give the test frequency. Some even give  series or parallel equivalent value. But many ignore the test voltage. Some of the designers use hit and trial method. They design the transformer, it works. To  make the specs,  they measure the  inductance values on the available instrument  say;  XYZ. May be this instrument is set to measure at 1.0 Vrms by default. When the vendor measures the same transformer with the available ABC  LCR meter, it is showing a different value. Could be in ABC LCR meter the test voltage is 0.3 V. Can we say that XYZ is good and ABC is bad. Both may be good. Only the difference could be  the test voltage.Vasavi's VLCRTZ comes with the variable test voltage and variable test frequency.  Verify the specs. These specs may or may not be sufficient for all the conditions. No single instrument can meet all requirements.
   
6. Simultaneous display of Q factor:  For some of the coils the Q factor is more important than the inductance value. For high inductance coils like CT's, the   Q factor will indicate the health of the coil. Irrespective of whether specified or not,  the manufacturer must make his own specs for Q factor based on his experience of the coils and tests. Vasavi's VLCRTZ is provided with two displays, one for L value  and the other for Q indication simultaneously.  Let us study the example of the ferrite CTs  with large number of turns. Suppose 1 to 2 adjacent tuns are shorted in the process. Can you check by testing resistance? Or inductance?  2  turns short in 5000 turns.Now  verify the inductance value. You will not find any difference in L value. The difference is negligible. Then how do you find  such a short? Observe the Q value with and with out shorting. You   will be surprised  to see that  the Q factor reduces by a large extent.  Thus you will be able to catch such usual  winding defects while testing L value alongwith Q factor. Now you may agree why you need  simultaneous display of Q factor.

 7. DC resistance Test: For transformer people the resistance means DC resistance. Most of the LCR meters come with AC resistance test. For non inductive resistors there is no problem. But for coils and transformers the windings have large reactance in series with the resistance. So the AC resistance measurement will be totally different from the DC resistance values. LCRTZ has both AC resistance and DC resistance tests.
 
8. Impedance matching transformers: The very name indicates  the importance of impedance measurement. The telecom transformers are specified to test impedance along with other parameters. For these types of coils and transformers, the impedance is the main parameter but the  inductance and resistance are the subsidiary parameters.  As the transformer and coil manufacturers use LCR meters without this test; the end users ignore or avoid giving this test to the manufacturers.  With Vasavi's LCRTZ  You can check the impedance at different test frequencies and test voltages.

9. RS232C Control of  LCRTZ  from PC (Option):
Let us imagine the usual method. Test with LCR meter, note down the readings, type the readings into the computer and then take the report. Each  job is done by a different person. There can be error at each stage. While reading, the technician may make error.  The operator's mind is recorded like a hard copy with the pass results and there is every chance of missing the rarely observed  fail readings. Apart from reading , the operator has to judge whether the readings fall  with in the limits or not.  When he  records, he may write 3 as 8, the recording error. Now these values are to be typed. Can not you have typing error?   Finally what is the result?  A mess of mistakes and  human errors. The entire exercise is for name sake only.
Now let us study the alternative. Imagine VLCRTZ with RS232C control. The limits along with test conditions  are  carefully set by a more experienced engineer once for all and stored  in a  file. To test the transformer, the operator has to load the file and connect the transformer to jig or connectors.  Any unskilled person can do the handling work.  The PC saves the test results into a database table, which you can use for taking reports or analysing the results. The operators efficiency will increase as he has not to strain his mind. Speed is increased  without loosing quality. Is this not a better choice?

10. System with 20 pin scanner :  For multi pin transformers you can consider Vasavi's CVCT-S20  an automatic  test system with scanning facility.   This system is very   ideal for testing   SMALL TRANSFORMERS like SMPS transformers, Telecom transformers (HYBRID, POT CORE, RM-CORE), Pulse transformers etc. The  testing  will  be very fast and fool proof. The  system  scans at  one stroke, all  the  windings of  a transformer .

11. System without scanning facility:  Even without having a scanner, you can have the luxury of transformer testing automatically. The operator's  job is to make the connections only. He need not  worry about readings. Instead of a scanner selecting the pins automatically, the operator is doing that job. But his burden of noting and  judging the reading is totally removed. The system consolidates all the defined  tests , displays the tested results and also  prompts you Go or No Go based on limits entered for each parameter. Further you can also save the data in to a  database table.

12.Testing  on sampling basis: This is a  notion by the  inward inspection and QC departments. Yes, they are right for  capacitors, resistors or semiconductors; because,  the manufacturing is done by automatic machines. Further the process lines also include 100% testing in the production chain itself. In the case of transformers and coils, they are generally  manufactured  by semiskilled  labour and are being handled by small manufacturers without having proper environment. So 100%   must be tested  both at the manufacturer and the end user.  The notion of sample testing should not be applied for transformers and coils.