NAI’s TC1 module offers a variety of advanced features tailored to meet the demands of wide-range temperature measurement applications, including the following:

NIST Thermocouple Interface Capability:

The TC1 function module features configuration programmability which provides interfaces for all standard NIST thermocouple types (J, K, T, E, N, B, R, and S), providing unparalleled versatility in thermocouple compatibility.

Self-Powered:

One standout feature of the module is its self-powered functionality, eliminating the need for external power sources and simplifying installation. This not only streamlines the setup process but also enhances its suitability for a wide range of applications.

Large Temperature Range:

The TC1 function module boasts an expansive temperature measurement range, reaching a remarkable 2300⁰C. This exceptional range makes it well-suited for applications where extreme temperatures are encountered, such as jet engines and gas turbine exhaust.

Up to ±0.2⁰C Accuracy:

With thermo-block compensation, the TC1 function module provides compensated measurements at accuracies up to ±0.2⁰C.

Optional Thermo-Block Compensation:

NAI offers an optional accessory (ACC-ISO-THERM-BLK2) which connects to the TC1 function module, allowing for automatic cold junction compensation temperature through an onboard RTD temperature sensor (CH8 will automatically configure to RTD mode if this accessory is used).

Programmable Sample Rate:

Users can set the sampling rate of the analog-to-digital converter (A/D) to match the specific needs of their application. This programmable sample rate ensures that data acquisition is optimized for accuracy and efficiency.

Offset Temperature:

The offset temperature feature provides users with the means to nullify system-induced measurement errors. This is crucial in achieving the highest level of measurement precision and reliability, especially in critical applications where accuracy is paramount.

While in thermocouple mode, the TC1 provides up to eight individual isolated thermocouple or low-voltage range A/D measurement channels. Configuration programmability provides interfaces for industry standard NIST thermocouple types (J, K, T, E, N, B, R, and S).

Thermocouples are widely used temperature-measurement devices because of their ruggedness, repeatability and fast response time. They offer a cost-effective means for measuring a much wider range of temperatures in comparison to other common solutions like resistance temperature devices (RTD), thermistors, or temperature-sensing integrated circuits (ICs). Although thermocouples can be used over a wider range of temperatures than RTDs and temperature-sensing ICs, they are far less linear. Also, RTDs and temperature-sensing ICs typically offer better sensitivity and accuracy. Thermocouple signals are very low-level and often require amplification or a high-resolution data converter to process the signals. Despite these disadvantages, overall cost, ease of use, and wide temperature range make thermocouples popular.

Thermocouples are constructed with two wires made from dissimilar metals. One wire is predesignated as the positive side, and the other as the negative. The industry standard NIST thermocouple types are defined by the metals or alloys used and the temperature range allowed for each type. Each thermocouple type offers a unique thermoelectric characteristic over its specified temperature range.

In Figure 1, the voltage generated by the loop is a function of the temperature difference between the two junctions. This phenomenon is known as the Seebeck effect which is described as the process in which thermal energy is converted into electrical energy. The Peltier effect is the opposite of the Seebeck effect which is the process of converting electrical energy to thermal energy. In Figure 1, the measure output voltage (V_OUT ) is a function of the difference between the measuring (hot) junction voltage and the reference (cold) junction voltage. Since V_HOT and V_COLD are generated by a temperature difference between the two junctions, V_OUT is also a function of this temperature difference. The scale factor, α (Seebeck coefficient), relates the voltage difference to the temperature difference.

Figure 2 illustrates the configuration most used in thermocouple applications. In this configuration, a third metal (known as an intermediate metal) such as copper, is introduced into the loop and the two additional junctions. In this configuration, provided the two junctions are at the same temperature, the intermediate metal type has no effect on the output voltage. This configuration allows the thermocouple to be used without a separate reference junction. V is still a function of the difference between the hot- and cold-junction temperature, related by the Seebeck coefficient. In this configuration, the cold-junction temperature must be known to determine the actual temperature measured at the hot-junction.

The simplest case occurs when the cold-junction temperature is at 0° C, also known as an ice-bath reference. At T_COLD = 0° C, V_OUT = V_HOT . In this case, the voltage measured at the hot-junction is a direct translation of the actual temperature at that junction.

When the cold-junction temperature is not at 0° C, the temperature of this junction must be known to determine the actual hot-junction temperature. The output voltage of the thermocouple must also be compensated to account for the voltage created by the nonzero cold-junction temperature. This process is known as cold-junction compensation.

NAI provides an optional accessory, NAI P/N ACC-ISO-THERM-BLK2, a thermocouple connection interface comprised of a separate isothermal interface/terminal block. The thermocouple sensors are connected to the accessory’s copper measurement wiring harness, allowing for automatic cold junction compensation temperature through an onboard RTD temperature sensor reporting the terminal temperature to a dedicated channel on the module (refer to Appendix A: Optional External Cold Junction Compensation Block Accessory).

In lieu of the External Cold Junction Compensation Block Accessory, a user supplied terminal connection block may also be used, provided the terminal temperature is measured and maintained in the manual cold junction compensation temperature register for proper compensation. A benefit of this would be the availability of Channel 8 for an additional Thermocouple or RTD measurement channel.

In addition to cold-junction temperature compensation, the TC1 provides the ability to program temperature offsets, which can be used to null out small temperature deviations from sensors or system interconnections as well as delta measurements from an initial temperature reading. The offset temperature is subtracted from the output temperature reading and may be configured individually for each channel.

The fundamental design of the TC1 is based on independent 24-bit Sigma-Delta A/D converters for each channel. This allows the TC1 to also be used for direct precision low voltage measurements (±78.125 mV) for uses in low-voltage range A/D applications (i.e. shunt resistor voltage/current sense measurements).

TC1 is designed for rugged embedded “on-the-move” or laboratory-grade environments, and provides continuous background built-in-test (BIT) capabilities for accuracy and “open” detection monitoring and flagging.

The module can measure low voltage dynamic signals in the microvolt range with faster update rates to 4800 Hz. Readings can track dynamic signals when high rates are selected, with some increase in noise jitter. Optimal accuracy and reading stability will be achieved by low update rate selections.

Default configuration runs periodic maintenance in the background for self-test and calibration at 30 second intervals, which briefly suspends reading updates during the performance of these routines. For time critical measurements, the periodic internal processes may optionally be suspended for continuous and uninterrupted readings. During this time, these maintenance operations may be triggered manually by the user at suitable intervals.

Automatic background BIT testing is provided. Each channel is checked at periodic intervals for correct A/D operation using an internal measurement of an on-board resistor reference. The open input detection test applies a low-level current pulse to the A/D converter inputs and tests for a full-scale 3.3V limit, indicating an open sensor circuit. Any failure triggers an interrupt if enabled, with the results available in the status registers. The testing is transparent to the user and has no effect on the operation of this module. Enabled by default at power on, it may optionally be disabled.

The TC1 provides the ability to program two temperature thresholds that will result in temperature alerts. For each threshold, a “low” and a “high” threshold value is specified that will be used to set the Temperature Alert statuses. The Temperature Threshold Low registers sets the threshold values to use to set the Temperature Alert Low status bit when the Temperature reading is below the low temperature threshold value. Conversely, the Temperature Threshold High registers sets the threshold values to use to set the Temperature Alert High status bit when the Temperature reading is above the high temperature threshold value. These threshold values are individually configurable on a per channel basis.

A possible usage of the two temperature thresholds is to use the first threshold detection levels as an early warning pre-alarm level and the second threshold detection levels as an alarm limit value. For this purpose, the Detect 2 thresholds should be set at larger deviation values from the nominal temperature than the Detect 1 thresholds.

For example:

(Threshold Low 2) < (Threshold Low 1) < (Nominal Temperature) < (Threshold High 1) < (Threshold High 2)

This allows the Detect 1 thresholds to serve as a pre-alert warning of temperature excursion, while Detect 2 may represent an alarm condition.

The TC1 Function Module provide registers that indicate faults or events. Refer to “Status and Interrupts Module Manual” for the Principle of Operation description.

The TC1 Function Module includes module common registers that provide access to module-level bare metal/FPGA revisions & compile times, unique serial number information, and temperature/voltage/current monitoring. Refer to “Module Common Registers Module Manual” for the detailed information.

The TC1 measurement registers provide Temperature measurements (in both Celsius and Fahrenheit degrees) and Voltage Measurements.

The TC1 control registers provide the ability to configure the channels to either Thermocouple or RTD mode and specifying the sample rate, Thermocouple type and Thermocouple temperature compensation settings.

The TC1 Temperature Threshold registers provide the ability to program two temperature thresholds that will result in temperature alerts.

Refer to “Module Common Registers Module Manual” for the register descriptions.

The TC1 Module provides status registers for BIT, Open, and Temperature Alert.

Refer to “Module Common Registers Module Manual” for the Module Common Registers Function Register Map.

BIT Status

Open Line Status

Temperature Alert Low 1 Status

Temperature Alert Low 2 Status

Temperature Alert High 1 Status

Temperature Alert High 2 Status

Summary Status

The Interrupt Vector and Interrupt Steering registers are located on the Motherboard Memory Space and do not require any Module Address Offsets. These registers are accessed using the absolute addresses listed in the table below.

When interrupts are enabled, the interrupt vector associated with the specific interrupt can be programmed with a unique number/identifier defined by the user such that it can be utilized in the Interrupt Service Routine (ISR) to identify the type of interrupt. When an interrupt occurs, the contents of the Interrupt Vector registers is reported as part of the interrupt mechanism. In addition to specifying the interrupt vector, the interrupt can be directed (“steered”) to the native bus or to the application running on the onboard ARM processor.

In most applications, limiting the number of interrupts generated is preferred as interrupts are costly, thus choosing the correct Edge/Level interrupt trigger to use is important.

Example 1: Fault detection

This example illustrates interrupt considerations when detecting a fault like an “open” on a line. When an “open” is detected, the system will receive an interrupt. If the “open” on the line is persistent and the trigger is set to “edge”, upon “clearing” the interrupt, the system will not regenerate another interrupt. If, instead, the trigger is set to “level”, upon “clearing” the interrupt, the system will re-generate another interrupt. Thus, in this case, it will be better to set the trigger type to “edge”.

Example 2: Threshold detection

This example illustrates interrupt considerations when detecting an event like reaching or exceeding the “high watermark” threshold value. In a communication device, when the number of elements received in the FIFO reaches the high-watermark threshold, an interrupt will be generated. Normally, the application would read the count of the number of elements in the FIFO and read this number of elements from the FIFO. After reading the FIFO data, the application would “clear” the interrupt. If the trigger type is set to “edge”, another interrupt will be generated only if the number of elements in FIFO goes below the “high watermark” after the “clearing” the interrupt and then fills up to reach the “high watermark” threshold value. Since receiving communication data is inherently asynchronous, it is possible that data can continue to fill the FIFO as the application is pulling data off the FIFO. If, at the time the interrupt is “cleared”, the number of elements in the FIFO is at or above the “high watermark”, no interrupts will be generated. In this case, it will be better to set the trigger type to “level”, as the purpose here is to make sure that the FIFO is serviced when the number of elements exceeds the high watermark threshold value. Thus, upon “clearing” the interrupt, if the number of elements in the FIFO is at or above the “high watermark” threshold value, another interrupt will be generated indicating that the FIFO needs to be serviced.

The examples in this section illustrate the differences in behavior of the Dynamic Status and Latched Status registers as well as the differences in behavior of Edge/Level Trigger when the Latched Status register is cleared.

Figure 1. Example of Module’s Channel-Mapped Dynamic and Latched Status States

The examples in this section illustrate the interrupt behavior with Edge/Level Trigger.

Figure 2. Illustration of Latched Status State for Module with 4-Channels with Interrupt Enabled

The registers in this section provide module information such as firmware revisions, capabilities and unique serial number information.