- Test frequency
- 20 Hz to 200 kHz on HG7729; 20 Hz to 300 kHz on HG7729A and HG7729B; 20 Hz to 1 MHz on HG7729C
- Scanning
- 20-channel transformer scan on all four models
- LCR parameters
- |Z|, |Y|, C, L, X, B, R, G, D, Q and phase, plus DC resistance, turns and phase
- Transformer scan parameters
- Turns ratio, number of turns, phase, inductance, capacitance, leakage inductance, quality factor, AC resistance, DC resistance, balance, pin short and LED
- Basic accuracy
- 0.05% for LCR and DC resistance; 0.1% for turns ratio
- Signal level
- 5 mV to 2 V for LCR tests, 5 mV to 10 V for the turns test, and 5 mV to 10 V as an option for LCR; automatic level 5 mV to 1 V
- DC bias
- Built in, ±5 V or ±50 mA, accuracy 1%
- Speed and storage
- 75, 20 or 6 measurements per second at 10 kHz and above; 100 setups inside and 500 on a USB drive
- Interface
- RS232C, USB TMC, USB CDC, HANDLER and GPIB, all supplied as standard
- Body
- 280 × 88 × 320 mm and 4.0 kg in the size drawing; 400 × 132 × 350 mm and about 10 kg in the parameter table
A transformer is not one component but a set of coupled windings, and the parameters that decide whether it works are spread across them: ratio, inductance, leakage, capacitance between windings and the resistance of each coil. Testing them one at a time is what a comprehensive tester is built to avoid.
Product overview
The range contains four instruments that share a 20-channel scanner, a full LCR engine and a transformer parameter set. What separates them is the frequency ceiling, which runs from 200 kHz in the base model to 1 MHz in the top one.
Everything else is common: the same accuracy for impedance and for turns ratio, the same built-in bias source, the same display and the same interfaces. That makes the choice simpler than the model count suggests, and it also means the frequency is the only real decision unless the fixture or the line imposes another.
The instrument drives one winding with a signal at a chosen frequency and measures the voltage and current at the terminals of that winding and of the others. From the ratios between them it derives the turns ratio and the phase relationship, and from the impedance it derives inductance, leakage inductance, capacitance and the loss terms.
The scanner is what makes this practical. It connects the instrument to the pins in a fixed sequence, so a transformer with several windings is measured in one pass. Each measurement is compared against a limit, and the instrument reports which bin the part belongs to.
The built-in bias source matters for the inductance reading. A magnetic core behaves differently depending on where it sits on its magnetisation curve, and a small-signal inductance measured without bias can be far from the value the circuit sees. Applying the bias current or voltage brings the core to the operating point before the measurement is taken.
The measurement is defined by its frequency and its level. Both are set per test, and both appear in the result, because an inductance quoted without them is not a specification of anything.
Start with the highest frequency at which any parameter has to be measured. That single figure separates the range: a part specified at a few hundred kilohertz at most fits the lower models, while a part with a specification at or near a megahertz needs the top one.
Then look at the parameters. If the test is a turns ratio and a winding resistance, the basic set is enough. If the part is characterised for leakage inductance, inter-winding capacitance, balance and pin continuity, the full scan set is what the fixture and the program have to cover, and the fixture becomes as important as the instrument.
Then consider the bias. A transformer whose inductance is specified at a DC bias cannot be checked without one, and the built-in source removes the external supply that would otherwise have to be wired into the fixture.
Then look at the line. The scan channels, the bin count and the handler interface decide how the part is presented and sorted; the serial, USB and bus interfaces decide who reads the result. Send the transformer drawing, the pin list, the parameters and the frequency at which each is specified, and a model, a scanner and a fixture can be quoted against them.
Measurement limitations and selection considerations
The instrument measures at its terminals, so the fixture is inside the measurement. Lead length, contact resistance and the capacitance of the scanner add to the values being read, and a fixture built for one transformer rarely suits another without correction.
The bias source has a limited range, and a part that needs more bias than the source can supply will be measured off its operating point. The material gives the range of the built-in source, and that range should be compared with the application before the instrument is chosen.
The frequency ceiling is a hard limit. A parameter specified above it cannot be measured on that model at all, and measuring at a lower frequency instead produces a different number rather than an approximation of the right one.
Finally, the accuracy figures apply under conditions the material does not state. The warm-up time and the calibration state are part of the measurement, and a comparison between instruments or between shifts is only meaningful when both are held to the same conditions.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
