Figure 5-6 Example of Measuring Turns Ratio in TRANSFORMER MODE. Wayne Kerr 3260B

5–8

Advanced Operation

Figure 5-6 Example of Measuring Turns Ratio in TRANSFORMER MODE

5.7.2 TRANSFORMER MODE Parameters

The following TRANSFORMER MODE parameters are selectable with the ten soft keys to the right of the display. Parameters which are common to both TRANSFORMER MODE and

IMPEDANCE MODE are described in section 4.7.2—IMPEDANCE MODE Parameters.

L + Q (Pri)

Measures the inductance (L) and quality factor (Q) of the transformer primary winding. The Equ cct parameter allows selection of either Parallel or Series resistance in the transformer primary winding. When Equ cct is set to Auto, the analyzer makes a measurement of the primary winding resistance and sets series or parallel equivalent circuit according to the following criterion:

Turns Ratio

Primary winding resistance >250Ω = Parallel equivalent circuit

Primary winding resistance <250Ω = Series equivalent circuit

Measures the turns ratio of a transformer. Turns ratio can be displayed as Np/Ns or Ns/Np. When maximum resolution is required, choose the display which is greater than unity. The value displayed is the ratio of measured voltages, hence non-integer results are likely. Trimming and high frequency lead compensation are not required for turns ratio measurements.

A negative reading when measuring turns ratio implies a reverseconnected winding. Check the winding sense convention.

Secondary turns (Ns) can be displayed. This requires the primary turns (Np) to be preset via the data entry keyboard. Allowable values of Np are between 0.001 and 10000.

For accurate measurement of turns ratio, software correction can

Advanced Operation 5–9 be employed when the primary impedance is high (typically

>50

Ω). A transparent primary leakage measurement is performed before the turns ratio measurement. Because this involves operating relays inside the 3260B, normal repetitive measurements are disabled with the ratio correction algorithm operating. Ratio correction is NOT automatically performed by the instrument.

Instead, the user must set it ON or OFF and define whether the transformer is a normal type (floating secondary) or an autotransformer (one end grounded) as this affects the loading corrections. This selection is made either from the SETTINGS page (see section 5.18), or by using keypad codes 14, 15 and 16 when in TRANSFORMER MODE or HANDLER MODE (see section 4.2.6.1). If the primary impedance is low, the turns ratio correction should be turned OFF. If a ratio correction option other than OFF is selected, it is displayed when Turns Ratio is selected in TRANSFORMER MODE.

For step-up transformers, the measured secondary voltage is limited to 10Vrms.

Rdc (Pri)

Rdc (Sec)

Leakage (Pri)

Leakage (Sec)

C (Pri–Sec)

Constant current drive is not provided for turns ratio measurements.

The series DC resistance of the transformer primary winding.

The series DC resistance of the transformer secondary winding.

The series leakage inductance and resistance of the transistor primary winding. Best results will be obtained by short-circuiting the transformer secondary winding(s). A message is displayed to this effect when the mode is initially selected. Leakage (Pri) and

Leakage (Sec) tests share the same measurement conditions.

The series leakage inductance and resistance of the transistor secondary winding. Best results will be obtained by shortcircuiting the transformer primary winding. A message is displayed to this effect when the mode is initially selected.

Leakage (Pri) and Leakage (Sec) tests share the same measurement conditions.

The capacitance between the transformer primary and secondary windings at the selected voltage and frequency test conditions.

Enters INSULATION MODE, see section 5.8.

INSULATION

The following TRANSFORMER MODE parameters are those displayed in the bottom lefthand-corner of the screen, shown in Figure 5-6. They are only visible when Hide Setup is NOT

SELECTED.

5–10

Drive Level

Equ cct:

Ratio

Advanced Operation

This parameter is available during measurement of L + Q (Pri),

Turns Ratio, Leakage (Pri), Leakage (Sec), C (Pri–Sec).

When Turns Ratio or C (Pri–Sec) is selected, only voltage drive can be set. All other settings listed above will accept either voltage or current drive, set by highlighting the parameter with the and

navigation keys, then altering the setting in pre-determined steps with the and navigation keys, or by using the data entry keypad. The range is:

L + Q (Pri);

Leakage (Pri);

Leakage (Sec).

1mV–10V 50µA–200mA

At frequencies above 300kHz the maximum current drive is restricted.

C (Pri–Sec).

Rdc (Sec).

(short circuit current 10mA)

See also ALC, in section 4.7.2—IMPEDANCE MODE Parameters

Available only for L + Q (Pri) measurements. Selectable between

Series, Parallel, or Auto. See L + Q (Pri), above.

Available only for Turns Ratio measurement. Selectable between

Np/Ns, Ns/Np or Ns Np=x, where x is a value between 0.001 and

10000.

See Turns Ratio, above.

5.8 INSULATION MODE (Optional)

Insulation tests can be made between transformer windings, and from each winding to the grounded metal case or shell of the transformer. For each transformer winding, the test voltage is applied to one BNC connector only, as indicated by the front panel LEDs. If 4-terminal operation is selected, this is the BROWN BNC connector (voltage sense low). For 2-terminal operation it is the RED BNC connector (drive current return). The active connections are shown in section 5.8.1—Connections.

The insulation test is a 3-terminal function. If measuring insulation between primary and secondary windings, any leakage to grounded terminals (e.g. the transformer case or shell) will be ignored. The insulation from either winding to grounded terminals may be separately measured, in which case primary to secondary leakage will be ignored. If a measurement of total leakage resistance between windings is required, make no connection to the ground lead

(i.e. the green clip lead).

Insulation tests are performed in single-shot mode with the Trigger control key being used to initiate each measurement. If the Trigger key is pressed and held, the analyzer will make