- Design and construction
- Repairs and initial testing
- Calibration procedure
- Temperature coefficient performance
- Summary & Conclusion
In today world we are surrounded by electric devices. Car, alarm clock, TV, phone or the very device you use to read this article, use electric signals to operate. Fundamental measure of electrical signal potential is voltage, and simplest form of it is direct current (DC) voltage. Voltage is measured in Volts, named after physicist Alessandro Volta. Devices that help us measure voltage are called voltmeters or if there are additional functions – multimeters. To make sure that measurement is correct and measurement is the same wherever you go is the job of metrology national and international organizations (such as PTB, NIST, NPL, and so on) that maintain and verify measurements accuarcy.
What do these labs use to maintain DC Volt for their own tests and comparisons? Main tool for such is DC Voltage Reference standards, manufactured by handful of the trusted vendors with decades of voltage realisation and measurement experience. Fluke Calibration have Model 732A and 732B as currently maintained products for this task, and we had a look on these already. These standards are pretty much industry standard, deployed worldwide to reproduce the DC Volt for laboratory and calibration uses.
In this article we will take a look on another DC reference specimen, Wavetek 7000, also known later as Fluke 7000 Volt Maintenance System. Wavetek 7000 is DC reference module designed as successor for older 4910 series units, with main focus on making unit portable and mobile. Shortly after Wavetek/Datron engineers designed Model 7000 system, Fluke acquired the metrology business of Wavetek and after the short production obsolete the line. Perhaps that was done to avoid internal competition with older Fluke 732A/732B and 734A reference lineup, even though 7004N/7010N system have superior feature set and performance equal or better to Model 734A 4-cell system. Also unlike 732/734 series, DC maintenance 7004/7010N systems had integrated null-meter to provide drift statistics and relative measurement functionality for ease of calibrations.
The heart of the Fluke 7000 is the fully isolated, compact LTZ1000-based zener cell with 10V and 1.018V DC Voltage output. Designed to be robust and portable, its internal batteries support short hot shipment and hot-plug. However, should complete power be lost (for example during international shipment), patented Reference Conditioning technology overcomes reference device hysteresis and restores the last powered value to the module. The 7000 modules also feature patented DC-DC convertor technology, which achieves unparalleled isolation from the external ACDC Line power adaptor. This makes the 7000 series particularly well suited to Josephson Junction direct comparison,as it speeds up intercomparison and reduces measurement uncertainty.
Ten, four and single housings are available for 7000 modules. The ten and four housings will accept either the Nanoscan or Transref units. The Nanoscan provides hardware averaging, a 4-wire buffer and remote control of its scan and measurement functions. The Transref provides a convenient hardware averaged output as well as the ability to access the output of individual modules using the Nanoscan System. The 70004T is an ideal product for support of transfers between single or multiple working standards at remote locations. Furthermore high isolation, low thermal EMF optical MOSFET technology is used to switch the output of each module through the housing backplane to the hardware average. Full reversal switching further ensures maximum rejection of thermal EMF offsets.
Just like other Wavetek/Datron metrology-level products, Model 7000 use best commercially available voltage reference, the Linear LTZ1000 . This LTZ1000 hermetic chip is considered as the best available zener reference by many engineers and industry experts.
Except rather brief user’s manual, there are no service or other manuals currently available for the 7000 Voltage Maintenance System so we are using this article to shed some more light onto design of Wavetek/Datron 7000 and 7000S scanner modules. These two parts were acquired from eBay. We tried to get nanoscan 7000N head for study and reverse engineering of the null-meter design, but somebody else bid higher.
|Fluke part number||Description|
|7000||10 V DC Reference (compatible with Model 7001, Model 7004N/7010N and Model 7004T/7010T)|
|7001||7000 unit in nicer enclosure, bundled with external 12V DC Power supply|
|7004T||4-reference Transref Volt Maintenance System with 12V DC Power Supply|
|7010T||10-reference Transref Volt Maintenance System with 12V DC Power Supply|
|7004N||4-Reference Nanoscan Volt Maintenance System complete with Low-Thermal Lead Set, Cabling for a second Nanoscan/Transref unit, Fiber-Optic RS232 Cabling, 12V DC Power Supply|
|7010N||10-Reference Nanoscan Volt Maintenance System complete with Low-Thermal Lead Set, Cabling for a second Nanoscan/Transref unit, Fiber-Optic RS232 Cabling, 12V DC Power Supply|
|7000S||10-Volt External Reference scanner Input Module (installs into a Model 7004N, 7010N, 7004T or 7010T chassis)|
|7050||Software – PC Windows™ based Software for Controlling 7004N/7010N Nanoscan Systems|
|7001-65||Ruggedized transit case complete with Environmental Monitor (for 7001 model)|
|7004-65||Ruggedized transit case with Environmental Monitor (for 7004 system)|
Table 1. Fluke/Wavetek 7000 ordering parts
Manuals and comparison to production standards
Product page now shows system is obsolete and requests to replace with Fluke 732B or 734A system instead.
Specification comparison with other production DC references standards:
|Specification||Wavetek/Fluke 7000 cell||Fluke 732A||Fluke 732B||Fluke 732C||Datron 4912|
|Output voltages||10 V, 1.018V|
|Stability (1y)||+60 ppm, -3 ppm||±2 ppm||±2 ppm||±1 ppm||±2 ppm|
|Stability (1y)||+60 ppm, -3 ppm||±2 ppm||±2 ppm||±1 ppm||±2 ppm|
|Temperature coefficient, ppm||<0.05 ppm/°C, <0.05 ppm/°C||±3 ppm||±1.5 ppm||<±0.1 ppm/°C||±3 ppm max (18-28°C)|
|Long term 1 year stability, ppm||? , ?||±8 ppm||±4 ppm||±0.5 ppm||±2 ppm|
|Max load current||100mA, 500µA||200 mA||600 µA||10 mA||418 mA|
|Construction type||Hermetic Fluke film networks||Precision wire-wound||Wirewound resistor in oil tank||Precision wire-wound|
|Active thermal compensation||Yes, +35 °C oven assembly||None||Thermistor in oil tank||None|
|Temperature sensor||Yes, 100 KΩ thermistor||No||No||Yes, 10 KΩ thermistor||No|
|Power requirements||AC mains or +12VDC 300mA||Not required, passive device|
|Backup/offline power supply||Internal 7.0 Ah +12V VRLA||Not required, passive device|
|Dimensions, weight||86 × 105 × 127 mm, 910g||254 × 206 × 311 mm, 4.8kg||86 × 105 × 127 mm, 730g|
|MSRP||Obsolete||$2222 USD||$3333 USD||$1111 USD||Obsolete|
Table 2. Hi-end DC Voltage Reference standards, brief specification list
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Repairs and initial testing
Longer test run with shield covers installed.
Test of two units
Comparison of Wavetek 7000’s to Fluke 732B
Beware, log may take some time and CPU resource to draw full SVG plot.
Here impact from unstable ambient temperature (due to air temperature from conditioner cycling) become obvious, as those “spikes” in measurement are correlated to the temperature variations.
Even simple towel blanket over the reference can help to reduce the impact significant enough to be visible on datalog:
Allan deviation plot on data shows that at short observation time τ, the ADEV is higher due to reference and meter noise. At longer τ, instability slightly decrease because the noise averages out. At still longer τ, the ADEV creep up again, suggesting that the meter stability is gradually drifting over time and impact from other factors.
If we to compare values from this ADEV graph to previous direct measurement plot of 3458A data alone, it become visible that half of the noise/instability actually caused by the meter itself. 3458A in delta mode of later graph is used on 100mVDC range, so any meter-sourced errors are attenuated, and Fluke 732B still provide lower noise/better stability than 3458A, so overall uncertainty of the measurement is improved.
Now that we confirm short term stability and noise, calibration was performed in differential operation to verified characterized Fluke 732B, that have assigned value with sub-ppm uncertainty.
Temperature coefficient performance
Summary & Conclusion
Cost breakdown for this project presented below:
|Wavetek 7000 cell||$1476||$40||eBay|
|Wavetek 7000 cell||$1300||$40||eBay|
|Wavetek 7000S scanner module||$118||$40||eBay|
|Total cost||$3014 USD|
Table 4. Costs summary
This Wavetek 7000 module will act as our travel transfer reference to maintain accurate 10V and 1V during annual calibrations and comparisons of different 732B units across the locations. Together with Fluke SL935 this kit is a great support for Fluke 5700A/5720A calibrators testing and artifact ACAL adjustments. Wavetek 7000 will be also used to get low uncertainty calibration in April 2019 after initial history collected.
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Modified: June 25, 2018, 11:43 p.m.