We have developed highly stable four terminal-pair capacitance standards of compact design. Their stability derives from using a ceramic dielectric and by keeping the standards at constant temperature using a two-stage oven.
Two BNC connectors are attached to the built-in platinum resistance thermometer (PRT) to monitor the internal temperature of the capacitor. Accurate capacitance measurement can be made via four terminal-pair coaxial BPO (MUSA) connectors. Each capacitor is housed in a metal box and requires only a simple 12 Volt DC supply to operate the temperature controller. A feature of this capacitor is that the value does increase by about 90 parts per million (ppm) with each factor of ten increase in the measurement frequency.
|
Capacitance |
Selected values between 50 pF to 1 μF available |
| Within a tolerance of ± 100 to ± 500 ppm depending on value, at 1 kHz | |
| Dissipation factor | Around 0·00005 to 0·0005 depending on value at 1 kHz |
| Frequency dependence | ~ 90ppm for each factor of 10 increase in measurement frequency |
| Drift | ± 0·05 ppm/day typically |
| Stability | (Short term) ± 0·01 ppm/hour |
| Max | Working voltage 30 V rms |
| Warm-up time | 1 hour (allow 48 hours to stabilise before use) |
| Operating ambient temperature | 15 °C to 24 °C |
| Relative humidity | 20% to 60% non-condensing |
| Storage temperature range | 5 °C to 70 °C |
| Power requirements | 12 V DC ± 0·5 V |
| Power consumption | 15 watts max. during initial warm-up, 2 watts after 1 hour, dependent on ambient temperature |
| Packaging | 93mm high, 123mm wide, 125mm depth, plus 50 mm height of BPOs |
| Weight | 1.4 kg |
| Warranty | 1 year return to base |
The best measurement capability, expressed as an expanded uncertainty (k = 2) is 70 ppm of nominal value, which applies to a wide range of instruments and test conditions.
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