User Interface

Display Type:240x64 graphics TFT LCD with LED back-light.
1x font is 4mm, 2x is 8mm.

Number of Inputs Displayed: One to Four.

Keypad: Sealed Silicon Rubber.

Temperature Display: Six significant digits, auto-ranged.

Display Update Rate: 0.5 Seconds.

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

Display Resolution: User selectable to seven significant digits.

Input Channels

There are four input channels, each of which may be independently configured for any of the supported sensor type.

Sensor Connection: 4-wire differential. DIN-6 Connector.

Sensor Types: See Supported Sensor Section.

Sensor Selection: Front Panel or remote interface.

Input Configurations: See input specifications table.

Sensor Excitation: Constant current: 1mA, 100mA or 10mA. Constant voltage: 100mV and 10mV RMS. Excitation Current: 1.0mA to 1.0µA, stepless.

AC Excitation Frequency: 1.25Hz bipolar square wave.

Maximum Resistance: 10mV = 10KΩ, 100mV = 1.0MΩ.

Thermocouples: Factory installed option on two channels only. All types supported.
Cold Junction compensation: internal, enable/disable.

Sample Rate: 15Hz per channel, all sensor types.

Digital Resolution: 24 bits.

Measurement Accuracy: See input specifications table.

Measurement Drift: 15ppm/°C.

Isolation: Input channel circuits are electrically isolated from all other internal circuitry but not from each other.

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.

CalGen™: Calibration curve generator fits any Diode or resistor sensor curve at 1, 2 or 3 user specified temperature points.

Status Outputs

Audible and Visual Alarms: Independent audible remote and visual alarms.

Relays: Two dry-contact relays. Both N.C. and N.O. contacts available.

Status reported via Remote Interface: Sensor fault, Heater over temperature fault.

Control Outputs

Number of Independent Control Loops: Two.

Control Input: Any sensor input.

Loop Update Rate: 15Hz per loop.

Isolation: Control loop circuitry is electrically isolated from all other internal circuitry.

Control Type: PID table, Enhanced PID, Ramp or Manual.

Autotune: Minimum bandwidth PID loop design.

PID Tables: Six user PID tables available for storage of setpoint and heater range vs. PID and heater range. 16 entries/table.

Set-point Accuracy: Six+ significant digits.

Fault Monitors: Control loops are disconnected upon detection of a control sensor fault or excessive internal temperature.

Over Temperature Disconnect: Heater may be relay disconnected from user equipment when a specified temperature is exceeded on any selected input.

Silicon Diode sensors use a fixed excitation current of 10µA and an input voltage range of 0 to 2.25V.

Negative and Positive Temperature Coefficient (NTC) / (PTC) resistor sensors are supported using a ratiometric bridge technique to cancel low frequency noise.

PTC sensor types include Platinum and Rhodium-Iron. These sensors are supported by a passive AC resistance bridge. Resistance ranges are: 100Ω, 1.0KΩ and 10KΩ.

The Model 24 provides robust support for the Negative Temperature Coefficient (NTC) sensors commonly used by cryogenic applications. They include Ruthenium-oxide, Carbon-Glass, Cernox™, Carbon Ceramic, Germanium and several others. Since these sensors have a negative temperature coefficient, the use of a 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.

The excitation source in the Model 24 is continuously variable so there are no significant steps in sensor self-heating. Voltage excitation values are 1.0V and 10mV. Excitation frequency is 1.25Hz.