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Model 54 Cryogenic Impedance Bridge

and Temperature Controller

Product Folder

  • Front Panel
  • Rear Panel


Highlights of the Model 54:

  • Four input channels, each capable of measuring resistance, mutual-inductance or inductance. Supported sensors include diode, resistance and mutual-inductance .
  • Operation from <10mK to over 1,000K with an appropriate sensor.

  • Expandable to 28 inputs by use of an Ethernet based distributed instrument connection.
  • Four Control Loops add high accuracy temperature control.

  • Large color display with touchscreen and full keypad.

  • Industrial grade security: Configurable firewall, HTTPS encryption and authentication.
  • Two dry-contact 10A relay outputs.

  • User programmable, web browser based Python editor and debugger.
  • Remote interfaces include Ethernet, USBA for data logging and a USBB serial port emulator. LabView™ drivers available, LXI Discovery.

  • National Instruments, Inc. LabVIEW™drivers are available for all interfaces.



Model 54 Rear Panel

  • Input Connectors: 6-pin circular snap-in recepticals provide 4-wire measurement connection plus a continuous shield through the backshell.
  • Loop #1:50-Watt heater output. Three-pin detachable terminal block.
  • Loop #2: 10-Watt heater, part of a 10 pin detachable terminal block.
  • Loop #3: 1.0-Watt heater, part of a 10 pin detachable terminal block.
  • Loop #4: 10 / 5.0-Volt output. Detachable terminal block.
  • Relay #1 and #2: Relay N.O. Contacts.
  • Ethernet / 2x USBA: RJ-45 with LAN activity indicator LEDs,USBA for external memory, mouse or keyboard.
  • USBB: Serial Port Emulator.
  • AC Power: RFI filtered Power Entry Module including fuse drawer and line voltage selector.



General Description

Cryogenic Impedance Bridge: The model 54 is a next generation four channel cryogenic impedance bridge capable of measuring resistance, inductance and mutual-inductance. Additionally, four control loop outputs support use as a temperature controller.

Each of the four input channels of the Model 54 is fabricated using a Cryo-con proprietary signal processing chip that measures impedance by use of an auto-blancing, ratiometric AC bridge. Here, advanced signal processing functions are built into a digital signal processor thereby replacing large amounts of analog circuitry with higher precision and more sophisticated digital algorithms.

Impedance measurement in cryogenic systems often requires low level excitation followed by precision signal recovery. To implement this, the Model 54 uses a differential voltage-mode excitation scheme followed by bi-phase lock-in detection. Differential mode excitation prevents electrical noise pickup currents from flowing through the sensor and the use of passive attenuation reduces the output impedance of the bridge, thereby reducing generated output noise. To further reduce noise, sine-wave excitation is used with programmable frequencies.

Cryogenic Thermometry: Negative-Temperature-Coefficient (NTC) resistors are often used as low temperature thermometers, especially at ultra-low temperature. The Model 54 provides robust support for these sensors by using constant-voltage AC excitation.

Since NTC sensors have high resistance at low temperature, measurement errors can be introduced by the lead capacitance in the sensor connections. The Model 54 eliminates this error by by recovering the complete AC signal vector and eliminating the capacitance component.

Another source of error at ultra-low temperature is sensor self-heating due to DC offsets produced by the measurement electronics. The Model 54 first measures the DC offset current flowing through the sensor then actively tracks and cancels it.

Ultra-low temperature measurements can be negatively affected by coarse steps in sensor excitation current. The Model 54 prevents this by using a step-less, continuously variable excitation source.

Positive Temperature Coefficient (PTC) resistor temperature sensors use the bridge in a passive excitation mode where a selected excitation is set and remains relatively constant over the entire measurement range.

Silicon diode sensors are also supported. This is done by switching out bridge functions and providing a 10µA DC constant-current excitation mode.

Errors in the conversion from measured data to temperature are reduced in all Cryo-con products by using a Cubic Spline interpolation algorithm. In addition to providing higher accuracy than conventional linear interpolation, the spline function eliminates discontinuities during temperature sweeps by ensuring that first and second derivatives are continuous.

Inductance and Mutual Inductance: Since the Model 54's bridge circuits are based on bi-phase lock-in detection, inductance and mutual-inductance measurements can be made to high accuracy. In this case, the bridge uses passive excitation with a user selected frequency up to 30Hz. The mutual-inductance based temperature sensors used in Milli-Kelvin level thermometry are directly supported.

Low Resistance By using a low noise preamplifier, high excitation current and bi-phase lock-in detection, the Model 54 can accurately measure resistance down to less than 10.0mΩ. Both R and Delta-R measurements are available

User Interface The Model 54’s user interface is based on a large, high resolution color graphics display with an integrated capacative touchscreen plus a full 20-key keypad. The Home screen projects four user configurable zones that allow the real-time display of all input channel, control loop and instrument status information. From this screen, accessing any of the instrument's configuration menus requires only a single key press.

Home Screen

Virtual Inputs The Model 54 can be expanded up to 28 input channels by connecting up to three Cryo-con temperature monitors to the Ethernet remote interface. Once connected, these virtual inputs appear to the Model 54 as additional inputs.

Four Temperature Control Loops To support flexible cryogenic temperature control applications, the Model 54 has four independent control loops. The Loop #1 heater output is a linear, low noise current source. Four full-scale ranges are available from 75W down to 500mW. Loop #2 is a three-range linear heater that will provide 10, 1.0 or 0.1-Watts. Loop #3 is a two-range linear heater with outputs of 1.0W or 100mW. Loop #4 is a non-powered voltage output.

Remote Control Standard Remote Interfaces include Ethernet, USBB and two USBA interfaces. The TCP and UDP data port servers bring fast Ethernet connectivity to data acquisition software including LabView™. Remote interfaces implement an IEEE-488.2 SCPI compliant remote command language that is easy to read and learn. LabView™ drivers are available for all remote interfaces.

User Programmable The Model 54 can be programmed by the user using the IPython scripting language. All functions of the instrument are available to the programming interface.



Ultra-Low Temperature Thermometry

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Specifications subject to change without notice. ©Cryogenic Control Systems, Inc. 1998 - 2022