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Features:
- AD8495 is an easy-to-use K-type thermocouple amplifier. It will convert the small voltage generated by the thermocouple junction into signal that analog-to-digital converter (ADC) or microcontroller can easily read. The gain from the thermocouple to the amplifier output is approximately 5 mV/°C.
- AD8495 uses on-chip temperature sensor for cold junction compensation. Thermocouples can measure in wide ambient temperature range.
- AD8495 built-in a precision instrumentation amplifier. The amplifier has high common-mode rejection performance that can suppress common mode noise that long lead thermocouples may pick up. For extra protection, the amplifier's high-impedance input terminal allows for easily adding additional filtering.
- AD8495 supports wide supply voltage range. Under a single 5V pwoer supply, AD8495 can cover nearly 1,000℃ thermocouple temperature range. Under 3V power supply, it can be directly cnected to low supply voltage ADC interface. It can also be power by up to ± 18V power supply, support industrial system that require wide common mode input range.
- Regardless of the power rails, AD8495 can easily measure negative temperature. It can uses voltage on reference pin to adjust the 0℃.
- Output, which provides the flexibility for adjusting AD8495 output range to adapt ADC.
- Stable input is designed to handle a variety of actual connection conditions. AD8495 can withstand much higher input voltage than supply rails. For example, under ± 5 V power supply, the voltage at the input, even to ±35 V, is guaranteed to not damage the device.
Application:
- J or K type thermocouple
- Oven temperature measurement
- Exhaust gas temperature detection
Specification:
- Material: Electrical components
Package List:
- 1 x Operational Amplifier Module
- 1 x Pin Header
- 1 x 2-Pin Socket
Dave Schaack
Reviewed in the United States on May 15, 2023
If you need a K-type thermocouple amplifier that has an analog output (instead of a digital output, which is a lot more common) there appear to be only two different small circuit boards available on Amazon for this purpose. There is this one, which is sold by itself (not bundled with a thermocouple), and there is Amazon product ID #B08C4Z9PZS, which is bundled with a thermocouple. Both of these boards are based on the Analog Devices AD8495 thermocouple amplifier IC, but the two boards are not identical. Both boards are generally of high quality construction, in my opinion.I have used both of these boards, and am reviewing both of them, each in their own product listing.This board, which is marked "CJMCU-8495" appears to be offered by many different vendors on Amazon, but at the time of this writing, only the vendor of this particular listing (# B07XG84RY9) has the board in stock in the U.S. In addition, only this vendor supplies a schematic of the board in the product listing. More about the schematic below.This board is supplied with the connectors for the thermocouple and the power and output connections, but those connectors are not soldered to the board. The user has to do that. In addition, I judge the terminal strip supplied for the thermocouple connection to be of low quality. That could be an issue if you need to connect and disconnect a thermocouple to the board a number of times.The supplied schematic is accurate except for one important detail. The schematic shows that the VREF terminal of the AD8495 is connected to a forward biased diode connected transistor, Q1. If that were the case, then the VREF terminal would be held at approximately +0.7 volts above ground, and that voltage would vary with the temperature of the board. In reality, VREF is connected to a voltage reference integrated circuit (TLVH 431), which produces a stable voltage of approximately +1.25 volts the way it is used.Because VREF is connected to +1.25 volts, the output of this board can cover the temperature range from approximately -250 degrees C to approximately +750 C with a 5 volt power supply. This is great if you need to measure negative temperatures. However, it also means that the output voltage is not referenced to ground; that is, 0 C temperature will produce an output voltage of VREF, not zero volts. And because VREF is not brought to an output pin, there is an additional uncertainty in the temperature measurement caused by the somewhat uncertain value of VREF, unless the user performs a calibration process.If you have the capability to do precise soldering on a surface mounted circuit board, you can short VREF to ground and then have a 0 C to 1000 C temperature range and O C corresponding to zero volts output with a 5 volt supply. That is the way I used it.An additional disadvantage of this board is that it has a single mounting hole. While that hole is large enough to pass a #4 screw, it means that the board tends to rotate around the screw when the thermocouple's leads are attached to the terminal strip.
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