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AVS-47B AC Resistance Bridge
Reliable Resistance Thermometry at Ultralow Temperatures
The AVS-47B is a proven, reliable cryogenic resistance bridge that has been designed for thermometry at low and ultralow temperatures. It offers sufficient accuracy and just the right features for this purpose, good price/performance ratio and a low total cost of ownership.
The original AVS-47 has gone through two major upgrades: from AVS-47 to AVS-47A and from revision "A" to revision "B". The latest improvements in "B" are:
1) The new AVS-47B is supported by a set of LabView VI:s. Using these VI:s, LabView owners (7.1 or later) can interface their AVS-47B directly with a PC, without need to have an GPIB bus + controller and without the additional cost of the the AVS47-IB computer interface. A free standard COM port is required. These VISA-based VI:s and an application note can be obtained from "Downloads".
2) The AVS-47B has a new isolated power supply for the primary computer interface. An external power supply is no longer needed in order to isolate the AVS-47B optically from the directly-interfaced PC.
3) The AVS-47B can be powered from any mains voltage between 90 and 250V (50-60Hz), from a safe 12V AC voltage source, or from two 12V batteries.
The earlier step in 2004 from the original AVS-47 to AVS-47A included two important changes:
1) With each of the eight input channels, user of an AVS-47A can decide, whether to ground the sensor either to the cryostat or to the preamplifier. If a sensor floats inside the cryostat, the channel is grounded to the preamplifier without danger of low-frequency ground currents. If the sensor is grounded to the cryostat (e.g. for better thermal contacts or for fewer filters and sensor wires), the corresponding channel is decoupled from the preamplifier ground, and any possible ground potential difference is arranged to appear as a common mode voltage across the differential inputs.
2) Addition of an automatic compensation circuit for the input capacitance. This is a relief to users that want to filter their sensor leads effectively in order to prevent high frequency interference from entering the cryostat. Active compensation makes the AVS-47A immune to at least ten times longer input time constant than before. One can now select larger capacitors for the filters.
Key Features of the AVS-47B
- Stable circuitry is based on null indicators and passive attenuators rather than on the gain of an AC amplifier. The AVS-47B needs very little calibration.
- Seven resistance ranges from 0-2 ohms to 0-2 Mohms. Capable of handling 2*100 ohms lead resistance on the lowest 2 ohms range and more on higher ranges.
- 8 multiplexed 4-wire input channels.
- Less ground loop problems than with the original AVS-47. Each channel can be individually grounded either to the cryostat or to the bridge.
- Active capacitance compensation circuit increases the allowed sensor capacitance up to
10 nF on the 2 Mohm range. Effective RF filtering against sensor heating is now possible.
- Seven excitation ranges
- Equivalent input noise voltage about 6 nV/sqrt(Hz), virtually no noise current.
- The low-noise preamplifier is located in a separate unit and can be mounted near to the cryostat with short leads to the sensors.
- Default operating fequency of about 13.7 Hz is suitable for both 50 and 60 Hz power systems.
- Possible low frequency interference at the sensor can be monitored, because the signal path is not filtered.
- 4 1/2-digit output from 0 to 19999
- 2.5 readings/second
- Stepless, calibrated analog output 0..+2V
- Mainly analog construction. The AVS-47B is built without using fast digital electronics. Very low RF emissions.
- The optional IEEE-488 "secondary" interface unit AVS47-IB is located outside the bridge, providing physical distance from the noisy bus. The low-speed, optically isolated "Picobus" cable between the AVS-47B and the interface can be filtered against RF, if required.
- The Picobus interface lines between the AVS-47B and AVS47-IB can be replaced by optical fiber lines ("Picolink" option, factory installation only).
- "No cost" optically isolated interfacing with a PC-computer running LabView 7.1 or higher is possible using the Picobus Primary Interface. A set of LabView Virtual Instruments (VI:s) is available for this.
- The AVS-47B has a universal power supply for 90..250V, but it can also be powered from two 12 V batteries or from a safe 12V AC voltage source.
Data Sheet and other information
Download the 10-page AVS-47B Brochure. (1.6 MB Adobe Acrobat PDF)
Download the 46-page AVS-47B Instruction Manual (2.2MB PDF).
Read a short desctiption about the PICOLINK optical fibre link option (HTML).
Download an 8-page article about AC Resistance Measurement in Presence of Input Capacitance. This article describes the problem, the automatic compensation circuit and its operation in detail. (375 kB Adobe Acrobat PDF).
Download the 23-page, 2.7MB PDF Application Note. about how LabView owners can interface the AVS-47B directly with a PC-type computer. Download the required "Set of VI:s."
PICOWATT (RV-ELEKTRONIIKKA OY)
VEROMIEHENTIE 14
FI-01510 VANTAA
FINLAND
