SPECIFICATIONS

AD8495

• The thermocouple signal is very small and must be amplified by considerable gain before it can be properly sampled by most ADCs. The AD8495 thermocouple amplifier provides a simple, low-cost solution for thermocouple temperature measurement. The integrated temperature sensor performs cold junction compensation. The fixed gain instrumentation amplifier amplifies the small voltage of the thermocouple to provide a 5 mV/°C output.

• The amplifier has high common-mode rejection and is capable of rejecting common-mode noise that may be picked up by long leads of thermocouples. For extra protection, the amplifier's high-impedance input allows for easy additional filtering.

• The AD849x output is a voltage proportional to the thermocouple measurement junction temperature (TMJ). To derive the measured temperature from the AD849x output voltage, use the transfer function TMJ=(VOUT−VREF)/(5mV/°C), VOUT=(TMJ×5mV/°C)+VREF. The AD8495 and AD8497 (Type K) instrumentation amplifiers have a gain of 122.4. With a single 5V supply, the 5mV/°C output allows these devices to cover a thermocouple temperature range of nearly 1000 degrees.

Product Parameter

• Reference pin provides offset adjustment

• Thermocouple disconnection detection

• Laser wafer adjustment to 1°C initial accuracy and 0.025°C/°C ambient temperature suppression

• Low power consumption: <1 mW (VS = 5 V)

• Rugged input withstands 4kVESD and provides overvoltage protection (OVP) up to VS±25V

• Linearity error less than ±2°C, this error is only caused by the nonlinearity of the thermocouple

 

Pin Description

• +IN: Positive input,

• -IN: negative input,

• VOUT: output

• REF reference input voltage: 1.24V, due to Q1 regulator limit, VCC maximum 18V, 5V recommended

• The registers allow the user to select settings such as a low-power mode for battery-powered applications, an adjustable digital filter for fast transient temperatures, and four individually programmable temperature alarm outputs that can be used to detect multiple temperature zones.

MAX6675 and MAX31855 are thermocouple temperature measurement chips widely used in industrial and embedded systems. Both chips support high-precision temperature measurement through the K-type thermocouple, and the internal integration of cold junction compensation and digital interface simplifies the design of the temperature acquisition system. Among them, the MAX6675 has a simple structure, and the maximum temperature measurement range is 0°C to 1024°C, which is suitable for medium and low temperature applications. MAX31855 is an upgrade that supports a wider temperature range (up to -270°C to 1800°C), higher resolution and sophisticated fault detection for more complex and demanding industrial environments. Both chips output digital signals through the SPI interface, which is easy to integrate with various microcontrollers or data acquisition systems, and are widely used in 3D printing, industrial temperature control, laboratory equipment and other fields.

Pin Description:.
VCC: power supply positive (typical 3-5v)
GND: Power supply ground (ground)
SCK: Serial clock input (SPI clock signal)
CS: chip select input, active low
SO: Serial Data Output (SPI Data Output)

Instructions for use:
The MAX31855 has cold junction compensation that converts the K,J,N,T or E type thermocouple signal into a digital quantity. The device outputs 14-bit signed data in a read-only format through a SPITM-compatible interface. The temperature resolution of the converter is 0.25 degrees, the high temperature reading is 1800 degrees, the low temperature reading is -270 degrees, and for the K-type thermocouple, the temperature range is -200 degrees to 700 degrees, maintaining an accuracy of ± 2 degrees.
MAX6675 a 12-bit resolution serial thermocouple analog-to-digital converter with cold junction compensation, linearity correction, and thermocouple break detection. 0 degrees ~ 1024 degrees of temperature measurement range, the converter temperature resolution of 0.25 degrees in-chip cold junction compensation. High impedance differential input. Thermocouple disconnection detection. Wide working voltage range 3.0~5.5V, working current 50mA. Operating temperature range -20 degrees ~ 85 degrees. 2000V ESD signal.