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Model 26C Cryogenic Temperature Controller


UpUp Model 26C General Specifications

User Interface

Display Type: 240x64 graphics TFT LCD with LED back-light.

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 types.

Sensor Connection: 4-wire differential.Six-pin snap-in connector..

Thermocouple Connection: External option. Field installable.

Sensor Types: See Supported Sensor Table.

Sensor Selection: Front Panel or remote interface.

Input Configurations: See input specifications table.

Bridge type: Ratio-metric resistance bridge.

Bridge Modes: Constant-Current or Constant-Voltage. AC or DC.

AC Excitation Frequency: 7.5Hz bipolar square wave.

Voltage Excitation: 10mV, 3.0mV, 1.0mV, 300µV, 200µV and 100µV. Minimum excitation current is <10nA, maximum is 1.25mA.

Sample Rate: 15Hz per channel.

Digital Resolution: 24 bits.

Measurement Accuracy: See input specifications table.

Measurement Drift:15ppm/oC. <10Ω or >10KΩ: 30ppm/oC.

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.

Data Logging

Data logging is performed to an internal 1,365 entry circular buffer and is time-stamped with a real-time clock. Buffer memory is non-volatile and will retain valid data without AC power. All four input channel temperatures are recorded.

User Setups

Four User Setups are available that save and restore the complete configuration of the instrument.

Control Outputs

Number of Independent Control Loops: Four.

Control Input: Any sensor input.

Loop Update Rate: 15Hz per loop.

Isolation: Control loop circuitry is referenced to chassis ground.

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.

Loop #1 Primary Heater Output

Short circuit protected linear current source.

Ranges: Four output ranges of 2.0A into a 25Ω load or 1.0A, 333mA and 100mA into 50Ω or less load.

Resolution: 5.0ppm of full-scale power (16 bits).

Readbacks: Heater output power, Heatsink temperature.

Connection: Detachable terminal block.

Loop #2 Heater Output

Short circuit protected linear current source.

Ranges: Three output ranges of 1.0A, 0.33A and 0.1A full-scale onto a 50Ω or less load.

Resolution: 5.0ppm of full-scale power (16 bits).

Readbacks: Heater output power, Heatsink temperature.

Connection: Detachable terminal block.

Loop #3 and #4 Control Outputs

Analog voltage outputs that are intended to drive an external booster supply.

Output: zero to 10 / 5.0-Volts. Output impedance: ~2,000Ω.

Resolution: 4.0ppm of full-scale power (16 bits).

Connection: Detachable terminal block.

Status Outputs

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

Relays: Two dry-contact relays. N.O. contacts available. Ratings are 125VAC @ 10A. Maximum switching power: 150W.

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

Remote Interfaces

Maximum reading rate for all interfaces is >40 rdg/s.

Ethernet: Connects to any Ethernet Local Area Network. Electrically isolated. TCP/IP and UDP servers provide remote control by using an ASCII command language. HTTP provides built-in web server. SMTP sends e-mail based on alarm conditions.

USB 2.0: serial port emulator. Data rates to 115,200 Baud.

IEEE-488.2 (GPIB): External Option, field installable.

Programming Language: IEEE-488.2 SCPI compatible.

LabVIEW™ drivers available for all interfaces.


Instrument firmware can be updated in the field via the Ethernet connection. Firmware updates are available via the Internet free of charge.


Ambient Temperature: 25°C ± 5°C for specified accuracy.

Mechanical: 8.5”W x 3.5”H x 12”D. One half-width 2U rack. Instrument bail standard, rack mount kit optional.

Weight: 6 Lbs.

Power Requirement: 90 to 240VAC, 50-60Hz, 220VA.

Conformity: European CE, RoHS.

Calibration: NIST traceable.

UpUpModel 26C Supported Sensors

A unique feature of the Model 26C is the use of a ratiometric AC resistance bridge to measure all types of sensors.

The AC excitation used with all resistor sensors (including Platinum RTDs) is a 7.5Hz bipolar square wave. This effectively eliminates DC measurement offset errors including the thermal EMF induced offsets that often occur in cryogenic systems.

Positive Temperature Coefficient (PTC) resistor sensors including Platinum and Rhodium-Iron RTDs use the resistance bridge in it's constant-current, AC operating mode. Platinum RTD sensors use a built-in DIN standard calibration curve that has been extended to 14K for cryogenic use.

The Model 26C's resistance bridge is used in a constant-voltage AC mode to provide 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.

An additional advantage to constant-voltage excitation 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 also improved.

The excitation source in the Model 26C is continuously variable so there are no steps in sensor self-heating.

Diode sensors are supported over their full temperature range by using the bridge in a DC, constant-current mode. This mode provides the required 10µA DC sensor excitation and 0 to 2.25 volt input range

Model 26C Supported Sensors
  Temperature Range Example Sensors
Diode 1.4 - 500K Cryo-con S900 / S950
SI-440, 430, 410
Lakeshore DT-670, 470
Platinum RTD 14 - 1,200K Cryo-con CP-100
Cryo-con GP-100
Cryo-con XP-100
Cryo-con XP-1K
Rhodium-Iron 1.4 - 800K Oxford PHZ 0002


4K - 300K

Vishay CLTS-2B

100mK - 400K AdSem, Inc.
Silicon Thermistor 2.0 - 720K AdSem, Inc.
Cernox™ 100mK - 325K Lakeshore, all types
Carbon-Ceramic 100mK - 300K Temati

Ruthenium-Oxide 100mK - 200K SI RO-600

Thermocouple 1.4 - 1,500K

All types.


Model 26C Input Specifications

Diode sensors
PTC resistor sensors
NTC resistor sensors


Excitation Mode
DC, Constant-Current
Constant-Current AC/DC
Constant-Voltage AC
DC voltage
Input Range
0.1V - 2.25V
1.0mA: 500Ω
100µA: 5.0KΩ
CLTS: 300Ω
Minimum: 5Ω Maximum: 100KΩ
 % of Rdg + % of Range
0.005% ± 80µV

0.01% ± 0.004Ω
0.02% ± 0.04Ω

14W to 30KΩ: 0.05% ± 0.04% 0.5Ω to 100KΩ: 0.15% ± 0.15%
  % of Range
Excitation Current
10µA DC
1.0mA, 100µA
10mV to 100µV,
1.25mA to 10nA,
continuously variable

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Specifications subject to change without notice. ©Cryogenic Control Systems, Inc. 1998 - 2021