Making Accurate Thermal Measurements at the Extremes with the MCP9604 Thermocouple Conditioning IC

Although the thermocouple was invented in 1821, which enabled the measurement of extremely high temperatures, it is intriguing that even after 200 years, industries continue to face challenges in rapidly designing systems capable of determining temperatures within 1°C. Many industries could benefit from a more intelligent integration of high temperature control including industrial furnaces and kilns, power plants, chemical and petrochemical industries, food processing and semiconductor manufacturing. This makes it equally interesting that most solutions only service one thermocouple. Enter the MCP9604 four channel thermocouple conditioning Integrated Circuit (IC) to help quickly integrate the signal chain, temperature measurement and math engine to directly result in a digital temperature of +/-1.5C maximum accuracy. Both its number of channels and accuracy make it unique. Capable of accepting the eight most common thermocouple types (including J and K), it simplifies costly in-line system production and integrates the common discrete components to instantly save on validation and calibration time.

This post will highlight some of the advantages and differentiators of the MCP9604 four channel thermocouple conditioning IC, such as:

• Being the first +/-1.5°C max four channel thermocouple conditioning IC
• Simplifying integration and accuracy with no external components required
• Reducing or eliminating the need for in-line system calibration
• Maintaining an accurate NIST ITS-90 (the International Temperature Scale of 1990) temperature

For the last 15 or so years, the IC industry has been working to integrate the thermocouple measurement circuit outside of the thermocouple itself. Discretely the signal chain for this circuit consists of 15 components including a precision ADC, a precision temperature sensor and a method of linearization to closely match an ITS-90 defined voltage to temperature relationship.

With the introduction of the MCP9604 quad channel conditioning IC, Microchip is building on our core competence from 2015, when we released the first single channel all-in-one thermal couple conditioning circuit. This new four-channel device continues to solve the ongoing challenges a discrete or multichip solution presents when measuring a thermocouple.

The first challenge when discussing temperature measurement is temperature accuracy. Being that some thermocouples read hundeds of degrees, the need for accuracy may be differenct for each end application. Does a kiln at 1100°C need to be tightly managed within 1°C? While that may be debatable, food preparation control at higher temperature is not debatable, especially for food safety and cooking consistency reasons.

Another challenge related to accuracy is adherence to measuring the small voltages of a thermocouple to calculate the tempearature associated with ITS-90. What makes this fascinating is that the relationship is not completely linear and it requires some subtle variation if the reading is to be more accurate. While many analog amplifier designs only specify accuracy to a single-order linear approximation of the ITS-90 (NIST defined) temperature, the MCP9604 adheres to higher-order poly nomial ITS-90 equations to maintain ±1.5°C maximum accuracy.

It is this delicate adherence of multi-polynomial voltage equation, in addition to a multicomponent design, that requires many systems designers to insert inline calibration techniques to yield the best accuracy possible. Alternatively, a fully integrated design, if done right, can take the need for part-by-part correction out of the production line. As a result, a well integrated part helps speed time to market and limit production variation while minimizing defects.

So, let’s recap where the introduction of the MCP9604 presents advantages to the designer…

A Unique Four Channel Thermocouple Conditioning Circuit

As there are many industrial applications with more than one thermocouple, the MCP9604 greatly similifies measurement circuits that present nontrivial challenges. Being the first four channel device for industrial would be impressive on its own, but the MCP9604 goes further in maintaining a 1.5°C maximum accuracy while measuring hundreds of degrees for harsh environments. In an industry filled with single channel solutions, the MCP9604 provides a +/-1.5°C max digital output that easily interfaces with microcontrollers and processors.

Maintaining an Accurate ITS-90 Temperature

As part of the measurement of thermocouple systems there is a need to relate voltage measurements back to the ITS-90 defined tables. The MCP9604 does much more than just present a single order linear relationship. It is measuring and adhering to (in some instances) up to ninth order polynomial approximations to report a tighter measurement accuracy.

Integration of Precision Components Without Need for More

The MCP9604 integrates and replaces the need for precision ADC, precision temperature sensor, amplifier and a math engine. Peviously, each previously discrete component would play an important role in measuring voltage, amplifying voltage and relatating it back to the room temperature. Now, only one MCP9604 is required to bring that value four times over, representing a tremendous bill of materials simplification.

No Tuning Necessary

An ancillary benefit to the MCP9604 is that there is no in-line calibration required. More simply put, because the MCP9604 is so accurate and stable, a manufacturing line does not require temperature point adjustments for thermocouple conditioning circuit variations. This consistency speeds up time to market for a manufacturing facility.

Final Thoughts

In summary, the MCP9604 provides value not available on the market today for thermocouple conditionaing ICs. If you have thermocouple applications such as industrial furnaces and kilns, power plants, chemical and petrochemical industries, food processing and semiconductor manufacturing, the MCP9604 offers a bill of materials reduction, greater accuracy without in-line calibration and adheres to NIST IST-90 voltage measurement tables for 8 thermocouple types.

For more information on purchasing the MCP9604 please go to the web page or contact Microchip sales to place an order. Another way to get started is to purchase the MCP9604 evaluation board, which will kick start your analysis by showing plotting measurements and showing configurable alert configuration option.

Figure 1 – MCP9600/MCP96L00 Block Diagram