Input Channels

The Model 18i has eight input channels where the Model 14i has four and the Model 12i has two. In every other way, the monitors are identical. Each input may be independently configured for any of the supported sensors. There is no use of scanning or multiplexing.

Sensor Connection: 4-wire differential. DB9 Connectors.

Sensor Types: See Supported Sensor Table.

Sensor Selection: Front Panel or remote interface.

Input Configurations: See input specifications table.

Excitation Modes: Constant-Current or Constant-Voltage.

AC Excitation Frequency: 1.625Hz bipolar square wave.

Voltage Excitations: 10mV. Minimum excitation current is 100nA, maximum is 1.25mA.

Sample Rate:15Hz per channel.

Digital Resolution: 24 bits.

Measurement Accuracy: See input specifications table.

Measurement Drift: 30ppm/^oC.

Isolation:Input channels are not isolated.

Measurement Filter: 0.5, 1, 2, 4, 8, 16, 32 and 64 Seconds.

Calibration Curves: Built-in curves for industry standard sensors plus eight user curves with up to 200 entries each. Interpolation is performed using a Cubic Spline.

User Programming

Users may program the instrument via the embedded web server. The IPython Notebook is used to edit, run and debug programs written in the Python language.

Security

Built-in firewall blocks any unused Ethernet service or protocol. Open HTTPS provides an encrypted and secure web server.

User Interface

Display Type: Graphics TFT LCD, 4mm and 8mm character height.

Number of Inputs Displayed: Up to eight.

Keypad: 4-key sealed Silicon Rubber.

Temperature Display: Six significant digits, autoranged.

Display Units: K, C, F or native sensor units.

Display Resolution: Up to seven significant digits.

Silicon and GaAlAs Diode sensors from Cryo-con or any other manufacturer are directly supported over their full 1.4 to 500K range using built-in calibration curves and sensor data. Plus, non-volatile Flash memory is available for several custom or calibrated sensors.

Platinum RTD sensors can use built-in DIN 43760 (IEC 750) standard setups for 100Ω or 1,000Ω devices. The DIN standard is used for temperatures from 70K to 1020K and extends it down to 30K for cryogenic use. A unique feature of Model 18i / 14i / 12i is the use of an AC ratiometric resistance bridge to cancel low frequency noise.

The Model 18i / 14i / 12i provides robust support for the Negative Temperature Coefficient (NTC) sensors commonly used by cryogenic applications. They include Ruthenium-oxide, Cernox™, Carbon-Glass, Germanium, Carbon-Ceramic and several others. Since they have a negative temperature coefficient, the constant-voltage measurement method will reduce, rather than increase, power dissipation in the sensor as temperature decreases. By maintaining the lowest possible power level, sensor self-heating is minimized and useful temperature range is greatly increased.

An additional advantage to constant-voltage biasing is that NTC resistors lose sensitivity in the upper part of their range. By auto-ranging excitation current to maintain a constant voltage, sensitivity and noise immunity in that range is greatly improved.

Sensor excitation used in conjunction with the constant-voltage feature is a 1.625Hz bipolar square wave. This effectively cancels thermal EMF induced offset errors that sometimes occur in cryogenic systems.