5091-6310E.pdf

Effective Multi-tap

Transformer Measurement

using a Scanner and the

Agilent 4263B LCR Meter

Application Note 1224-5

Introduction

Agilent 4263B Transformer

Measurement Capability

With the progress of recent electronics equipment and

digital networks, production amounts are increasing

of the transformers which contribute to equipment

miniaturization, low power dissipation and higher quality.

Therefore, improvement of select estimate efficiency is

required at the production line or incoming inspection.

Noticed recently, improvement of estimation efficiency is

required for pulse transformers which are used in LAN

or ISDN digital networks, and for multi.-tap transformers

with three or more pole taps, such as switching power

transformers. This application note shows an effective

multi-tap transformer measurement using a scanner

and the Agilent 4263B LCR meter.

The 4263B LCR meter is a low price instrument which

measures the fundamental parameters of LCR components

with speeds as fast as 25ms, at frequencies of 100, 120,

1k, 10k and 100kHz, In addition, with option 001, the

4263B measures turns ratio (N), mutual inductance (M)

and dc resistance (DCR) which are required for

transformer measurement. Figure 1 shows a 4263B

simple block diagram for L, M, and DCR measurement.

For example, in the inductance-turns ratio (L-N)

measurement, an ac voltage is applied at the Hcur

terminal. Self-inductance value (L1) is calculated from

the measured values of V1 and I1. Turns ratio (N) is

automatically obtained from the ratio of measured values

V1 and V2 (discriminating the polarity simultaneously).

In the dc resistance (of L-DCR) measurement, the applied

voltage at the Hcur terminal is dc. Dc resistance value

(DCR1) is calculated from the measured values V1 and I1.

There are, however, the following limitations when using

the measurement connection.

• Only primary self-inductance and dc resistance of

the transformer can be measured. For the secondary

values, the transformer connections must be changed.

• Turns ratio must be 0.9 or more (In the case of less

than 0.9, the measurement is not performed due to

saturation of internal circuitry).

Agilent 16060A transformer test fixture can be used

to overcome these limitations. By changing the external

switch of this fixture, connections to the transformer

are changed and thus both primary and secondary

parameters and turns ratio can easily be measured.

Figure 2 shows the simple block diagram of the 16060A.

Figure 1. Agilent 4263B block diagram for L, M, and DCR measurement

Figure 2. Agilent 16060A block diagram

Multi-Tap Transformer Measurement

Using a Scanner

Multi-tap transformers having two or more poles can be

measured with the 4263B and a scanner.

(B) System construction recommendations

When constructing the system, the following points must

be considered to assure the measurements are as precise

as can be. (See figure 5)

(A) System configuration

Figure 3 shows the system configuration for measuring a

multi-tap transformer that has 4 taps.

1.Make measurement cables as short as possible. The

parasitic inductance and resistance of measurement

cables make a large contribution to measurement

error. For recommendable length, conductive wire

inductance value must be 1/10 or less than the

measured inductance value (similarly conductive

wire resistance).

The Agilent 3488A switch/control unit with a 4 x 4

matrix switch module (Opt. 013) is used. Option 013

offers highly flexible switching, and any combination of

4 input channels may be connected to any combination

of 4 output channels. Thus option 013 is suitable for

testing the multi-tap transformer. Figure 4 shows the

hardware configuration of the 4 x 4 matrix switch

module.

2.Configure into a shielded 2 terminal configuration,

to prevent the influence of external noise or stray

capacitance.

3.Connect the low terminals close to the transformer.

In the 4263B transformer measurement, the primary

and secondary inductors’ low terminals of the

transformer must be connected together. When

using a scanner, these connections should be close to

the transformer under test. If connecting at a far point

from the transformer (for example, input point of

scanner module), low side wire resistance would

contribute to increase measurement error.

Figure 3. System configuration for multi-tap transformer

Figure 4. Option 013 4 x 4 matrix module

Figure 5. System construction

All measurements of the multi-tap transformer,

self-inductance, dc resistance, and turns ratio, can be

measured with only one connection by using the sample

program shown at the end of this note ( for HP 9000

Series 300 Controller). Figure 6 show the flow chart of

the sample program.

Figure 6. Flow chart of sample program

This program executes the open and short corrections

and displays each measured value of each tap of the

transformer. If turns ratio measurement cannot be made

due to the condition that turns ratio must be 0.9 or

greater, the scanner will be automatically changed and

the measurements re-done. This program can be modified

to match other systems or conditions.

The following steps outline the program procedure:

Step 1. Run the program. The following message is

displayed on the controller’s display.

Selection (1) Measurement (2) Correction ?

Type number and press RETURN key

Figure 7. OPEN Condition

At this point, select the measurement directly , or first

the measurement of correction data. To execute the

measurement, type 1 and press RETURN key on the

controller (Go to step 4). To measure the correction data,

type 2 and press RETURN key on the controller.

Step 2. If the measurement of correction data in step 1

was selected, the following message is displayed

on the controller’s display. The open correction

data of each channel of the scanner (CH.0-CH.3)

is now measured.

CH.0 Open measurement

Open test terminals of CH.0

Start open meas. (2) Skip CH.0 open meas?

Type number and press RETURN key

To measure the open correction data, set all channels

to the open condition as shown in figure 7. Then, type 1

and press RETURN key on the controller. Open correction

data of channel number 0 (CH.0) is acquired. Continue

to acquire data for channels 1 - 3.

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