AT3600 User Manual

7.1 Available Transformer Tests and Test Conditions

7.1.1 Application Of Tests

The following table summarizes the tests available for the AT3600 and indicates where they might be used:

Test	Description	Main Application	Winding Tested	Reason for Test
CTY	Continuity	All transformers	�	Properly installed fixture
R	DC Resistance	All transformers	All windings	Properly installed fixture Correct wire used Integrity of terminations
LS	Inductance (Series circuit)	Most transformers But usually not line frequency transformers	One winding usually the primary	Correct primary turns Right grade of core material Core correctly assembled
LP	Inductance (Parallel circuit)
QL	Quality Factor			�
RLS	Equivalent Series Resistance			Right grade of core material Core correctly assembled Check for shorted turns
RLP	Equivalent Parallel Resistance
D	Dissipation Factor
LL	Leakage Inductance	SMPS transformers Communication transformers Others as applicable	Selected windings	Check windings have been installed in the correct position relative to the core
LLO
C	Interwinding Capacitance	High frequency transformers Isolating transformers	�	Check winding positioning Check insulation thickness between windings
TR	Turns Ratio and Phasing	Most transformers, but usually not line frequency transformers	All windings	Check windings have correct turns and phasing
TRL	Turns Ratio by Inductance	As with Turns Ratio but used where there is poor flux linkage between windings.	All windings	Check windings have correct turns and phasing
MAGI	Magnetising Current	Usually line frequency transformers	One winding, usually the primary	Correct primary turns Correct core material properly assembled
MAGX	MAGI (External Source)
VOC	Open Circuit Voltage		All other windings	Correct secondary turns Correct phasing
VOCX	VOCX (External Source)
LVOC	Low Voltage Open Circuit
IR	Insulation Resistance	All transformers	Between selected windings	Winding isolation check where safety is not involved
HPDC	Hi-Pot (DC)	All transformers especially those used for safety insulation	Between selected windings usually primary to secondary, screens and core	High voltage safety insulation
HPAC	Hi-Pot (AC)
LSB	Inductance with Bias Current (Series Circuit)	Transformers for use in applications where passing significant (dc) bias current is part of the normal operation	One winding	Correct number of turns Right grade of core material Core correctly assembled
LPB	Inductance with Bias Current (Parallel Circuit)
WATT	Wattage	50Hz Iron core transformers	One winding	Correct core material Properly assembled
WATX	WATT (External Source)
SURG	Surge Stress Test	All transformers, especially those using fine wire	Selected windings	To identify shorted turns
TRIM	Trimming Adjustment	Transformers with variable / trimmable components	�	To adjust transformer to give specific measured values
OUT	Output To User Port	�	�	Allows the AT to perform external switching as part of the test program.
R2	DC Resistance Match	SMPS, audio & telecom	All windings	Checks matching between windings
L2	Inductance Match	SMPS, audio & telecom transformers	All windings	Checks matching between windings
C2	Capacitance Match	SMPS, audio & telecom transformers	All windings	Checks correct winding position on bobbin
GBAL	General Longitudinal Balance	Audio & telecom transformers	Selected Windings	Checks common mode rejection ratio
LBAL	Longitudinal Balance	Audio & telecom transformers	Selected Windings	Checks common mode rejection ratio
ILOS	Insertion Loss	Audio & telecom transformers	Selected Windings	Checks losses within the transformer
RESP	Frequency Response	Audio & telecom transformers	Selected Windings	Checks losses over a range of frequencies
RLOS	Return Loss	Audio & telecom transformers	Selected Windings	Checks losses returned by a transformer
Z	Impedance	Audio & telecom transformers	Selected Windings	Checks impedance at a given frequency
ZB	Impedance + bias	Audio & telecom transformers	Selected Windings	Checks impedance at a given frequency
STRW	Stress Wattage	Line frequency & High Frequency Transformers	One Winding (Usually the primary)	Checks integrity of inter-turn insulation, the magnetic material and joints
STRX	STRW (External Source)
ANGL	Impedance Phase Angle	Audio & telecom transformers	Selected Windings	Finds phase shift between Voltage and Current on a winding.
PHAS	Interwinding Phase Test	Audio & telecom transformers	Selected Windings	Measures phase shift between a pair of windings
ILK	Leakage Current Test	Medical applications	Between Primary and Secondary Windings	Checks for a common mode current due to capacitance
LSBX*	Inductance with External Bias (Series Circuit)	Wound components that usually carry a significant DC Bias current in normal operation.	Selected Windings	Checks number of turns, right grade of correctly assembled core material, where bias current is greater than LSB test can handle.
LPBX*	Inductance with External Bias (Parallel Circuit)	Wound components that usually carry a significant DC Bias current in normal operation.	Select Windings	Checks number of turns, right grade of correctly assembled core material, where bias current is greater than LPB test can handle.
ZBX*	Impedance with External Bias	Audio & Telecom	Select Windings	Checks impedance at a given frequency, while applying a greater bias current than is possible with ZB test.
ACRT	Hi-Pot Ramp (AC)	All transformers especially those used for safety insulation	Between selected windings usually primary to secondary, screens and core	High voltage safety insulation
DCRT	Hi-Pot Ramp (DC)
ACVB	Voltage Breakdown (AC)	Transformers with MOV fitted	Between selected windings usually primary to secondary, screens and core	High voltage safety insulation
DCVB	Voltage Breakdown (DC)

* These tests require the use of one or more Voltech DC1000 Precision DC Bias Current Sources. Contact your Voltech sales office for details.

SELF RESONANT FREQUENCY

Practical inductive components are not perfect inductors; they have stray resistances and capacitances associated with them. For certain components, especially those with a low inductance value, the impedance of the stray capacitance can become significant when compared to that of the inductance.

X_L = 2πf_L �������� X_C = � πf_C

At a sufficiently high frequency, the capacitive impedance can dominate, making a measurement of the inductance impossible. Under these circumstances, any measurement instrument may report negative inductance values and measurement errors. Should these symptoms be observed, reduce the test frequency to avoid problems.

The frequency at which the inductive impedance equals the capacitive impedance (X_L = X_C) is known as the self resonant frequency (SRF) of the component. At this point, the phase angle of the impedance (which can be measured using the ANGL test) is zero. At test conditions where the frequency is low enough for problems with capacitive impedance to be negligible, the phase angle will be positive and close to 90 degrees. Therefore an ANGL test can be used during program development to confirm if measurement problems are due to the chosen test frequency approaching the SRF of the part under test. If the angle is significantly less than 90 degrees, consider reducing the test frequency.

Note that stray fixture capacitance will add to the capacitance of the component and reduce the SRF. Performing compensation will remove the effect of stray fixture capacitance on the measurement of capacitance, but cannot remove its effect on SRF.