 MODEL 12
Low Voltage
Thermal
Converter
...the only instrument available for true NIST traceable calibration of digital multimeters in the range from 2 millivolts to 200 millivolts
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Accurate calibration of low AC voltages presents several challenges not encountered at voltages above 1 volt. The
introduction of new high resolution high acccuracy AC digital voltmeters with band widths up to a megahertz requires
improved calibration standards.
The Holt LOW VOLTAGE THERMAL VOLTAGE CONVERTER, Model 12, is designed to meet these challenges while
adhering to Holt's principle of extending the known state of the art of conservative metrology. This device is a passive
TVC based on the principle of the Micro Potentiometer which was developed by Myron C. Selby at the National
Bureau of Standards in 1951. The original micropots were developed for the generation of low voltages at
frequencies to 1000 MHz. Holt has adapted this technique to a multi range TVC which provides continuous coverage
of voltages from 1 millivolt to 200 millivolts at frequencies from 6 Hz to 1 MHz.
The AC/DC differences are very small and stable and the uncertainties are as low as NIST traceability will allow. A
passive instrument with no amplifiers, the long term stability of the Model 12 is a function of it's vacuum thermoelement and thick film resistors. The AC/DC difference is not a function of applied voltage level so that ranges can
be inter-compared for long term stability eliminating the need for frequent recalibration. When used with the Holt
Model 68 Thermal Transfer Voltmeter as the readout device a constant resolution of better than 5 ppm is provided.
The LVTVC provides stable output voltages at the frequency desired with low output impedances. The loading factor
is less than 0.1% at 1 MHz when calibrating an instrument like the Hp 3458A at 100 millivolts. This loading factor is
easily measured and a correction factor may be used to compensate if even higher accuracy is desired.
Used with the Holt Model 68 low voltage calibration may be automated under IEEE488 control.
See below for the technical specifications of the Model 12 LVTVC.
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MODEL 12 LOW VOLTAGE THERMAL VOLTAGE CONVERTER
TECHNICAL SPECIFICATIONS |
OUTPUT VOLTAGES
The Model 12 provides seven output voltage ranges with the following full scale voltages:
200 mV., 100 mV., 50 mV., 20 mV., 10 mV.. 5 mV., and 2 mV. Each range is usable from 120% to 40% of full scale.
TYPICAL AC/DC DIFFERENCES
The table below shows typical AC/DC differences of the Model 12. The frequency response curves of each range are
the normal smooth responses of a resistive element with low inductance and a small capacitive load. There are no
second order resonances or discontinuities. List price includes NIST traceable data at the points shown.
 | Click icon on left to see typical AC/DC difference in PPA. |
| INPUT VOLTAGE | The Model 12 is driven with an input of approximately 10 volts RMS for full scale output on any range.
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| INPUT IMPEDANCE | 2000 Ohms resistive
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| THERMOELEMENT PROTECTION | The thermo-element is protected from burn out or overload damage for input voltages up to 100 volts RMS
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| THERMO-ELEMENT OUTPUT VOLTAGE | 7 mV DC at rated full scale on any range
DC Reversal Error less than 50 ppm
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| CONNECTORS | Input and output connectors are Coaxial type N
Thermo-element output connector is a two pin MS 3102A-10SL-4P
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 | Click icon on left to see simpified schematic circuit diagram. |
Specifications subject to change without notice.
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