32-Channel USB/IP Based Thermocouple Data Acquisition System

The OMB-DAQ-TC-RACK and OMB-DAQ-TC-RACK-EXP32 offer exceptional performance and accuracy for thermocouple measurement applications at a low cost per channel. Offering both Ethernet and USB ports, the OMB-DAQ-TC-RACK provides 32 channels of 24-bit resolution for medium channel installations. The OMB-DAQ-TC-RACK-EXP32 adds 32 high-precision channels to support larger installations. Accuracy is designed into the product with sigma-delta 24-bit ADCs, differential inputs, thermocouple-to-host isolation and cold-junction compensation (CJC) for each channel to reduce the effects of thermal gradients. With digital alarming notifications when a temperature exceeds programmed limits, the OMB-DAQ-TC-RACK and OMB-DAQ-TC-RACK-EXP32 offer the perfect solution for temperature monitoring applications including server rooms, refrigerated storage, and long-run test cells.

Specifications
(Typical for 25°C (77°F) unless otherwise specified)
These specifications apply to both the OMB-DAQ-TC-RACK and OMB-DAQ-TC-RACK-EXP32 unless noted otherwise.
Thermocouple Input
A/D Converter Type: Delta-Sigma
A/D Resolution: 24-bit
Number of Channels: 32 (64 when OMB-DAQ-TC-RACK is connected to OMB-DAQ-TC-RACK-EXP32)
Filtering Options: 50 Hz or 60 Hz noise filtering, software-selectable
Isolation Between Any Thermocouple Input Channel and Chassis Ground: 500 Vdc absolute max
Channel Configuration: Software-selectable to match thermocouple sensor type
Differential Input Voltage Range: ±78.125 mV
Absolute Maximum Input Voltage (Between any Two TCx Inputs): ±25V (power on), ±25V (power off)
Differential Input Impedance:
    50 Hz Filtering, Power On: 26 M?
    60 Hz Filtering, Power On: 20 M?
Input Current:
    Open Thermocouple Detect Disabled: 2 nA
    Open Thermocouple Detect Enabled: 75 nA
Common Mode Rejection:
    50 Hz Filtering at DC and f_IN=50 Hz: 110 dB
    60 Hz Filtering at DC and f_IN=60 Hz: 110 dB
Noise Rejection:
    50 Hz Filtering at f_IN=50 Hz: 80 dB typ
    60 Hz Filtering at f_IN=60 Hz: 80 dB typ
Input Bandwidth:
    50 Hz Filtering: 22 Hz
    60 Hz Filtering: 26 Hz
Crosstalk Between Any Two Thermocouple Inputs: -90 dB
Sample Rate: 3 Hz max (per channel); the enabled thermocouple inputs are continuously converted at the maximum A/D converter rate
Common Mode Voltage Range:
    TCx Channel to TCx Channel: ±1.40V
    TCx Channel Relative to Chassis Ground, f_IN = 60 Hz: ±3.5 Vac p-p
    TCx Channel Relative to Chassis Ground: ±48 Vdc
When thermocouple sensors are connected to different common mode voltages, the channels with floating thermocouples sensors are biased to approximately the average value of the applied common mode voltages. Each of the applied common mode voltages must then be less than or equal to the average common mode voltage ±1.40 V or [CMVapplied = (CMVaverage ±1.4 V)].
Input Noise (50 or 60 Hz Filtering): 510 nV rms
Gain Error (50 or 60 Hz Filtering): 0.004% FSR
Offset Error (50 or 60 Hz Filtering): 3 µV
Measurement Sensitivity (Smallest Change in Temperature That Can Be Detected):
    Thermocouple Type J, K, T, E, N: 0.05°C
    Thermocouple Type R, S: 0.10°C
    Thermocouple Type B: 0.15°C
Warm-Up Time: 20 minutes min
Open Thermocouple Detect Response Time: 1 s
CJC Sensor Accuracy (0 to 45°C): ±0.20°C typ, ±0.40°C max
Channel Configuration
Thermocouple (J, K, T, E, R, S, B, N): 32 differential channels Channel configuration is stored on EEPROM external to the isolated microcontroller by the firmware whenever any item is modified. Modification is performed by commands issued from an external application, and the configuration is made nonvolatile through the use of the EEPROM.

Digital Input
Number of Inputs: 8 channels (16 when OMB-DAQ-TC-RACK connected to OMB-DAQ-TC-RACK-EXP32)
Configuration: Fixed input
Input Voltage Range: 0 to 15V
Input Type: CMOS (Schmitt trigger)
Input Characteristics: 100 k? pull-up resistor, 28.7 k? series resistor
Maximum Input Voltage Range: 0 to 20V max (power on/off, relative to IGND pins)
Pull-Up Configuration: All pins pulled up to 5V via individual 100 k? resistors using slide switch SW5; SW5 default position are on (pulled up)
Transfer Rate (Software Paced): 500 port reads per second typ
Input High Voltage: 1.3V min, 2.2V max
Input Low Voltage: 1.5V max, 0.6V min
Schmitt Trigger Hysteresis: 0.4V min, 1.2V max

Digital Output
Number of Outputs: 32 channels, shared with alarms (64 when OMB-DAQ-TC-RACK connected to OMB-DAQ-TC-RACK-EXP32)
Configuration: Open drain output
Output Characteristics: 100 k? pull-up, open drain (DMOS transistor)
Pull-Up Configuration: All pins pulled up to 5V through individual 100 k? resistors using slide switches SW1-SW4; the default positions for SW1-SW4 are on (pulled up)
Transfer Rate (Software Paced): Digital output–500 port writes per second typ
Output Voltage Range:
    0 to 5V: Internal 100 k? pull-up resistors connected to 5V by default
    0 to 15V: Max (using external pull-up resistor)
Ground: Pins labeled IGND are isolated from AGND and chassis ground
Off State Leakage Current: 0.1 µA
Sink Current Capability: 100 mA max (continuous) per output pin
DMOS Transistor On-Resistance (Drain to Source): 4 O

Environmental
Operating Temperature Range: 0 to 45°C (32 to 113°F)
Storage Temperature Range: -40 to 85°C (-40 to 185°F)
Humidity: 0 to 90% RH non-condensing
Mechanical
Dimensions: 482.6 L x 128.6 W x 43.18 mm H (19 x 6.15 x 1.74")
Weight: OMB-DAQ-TC-RACK: 3.8 lb (1.73 kg); OMB-DAQ-TC-RACK-EXP32: 3.2 lb (1.45 kg)