Analog option¶

In contrast to the digital Option, to measure a analog signal from the thermocouple, more components are necessary. The Orange LED lights up when the analog channel is used.

Thermocouple Amplifier¶

The thermocouple amplifier AD8485 amplifies the signal to a single line analog signal. This circuit also includes a cold junction compensation with an internal temperature sensor to reduce this effect. For more informations about the cold junction effect, read here.

ADC Driver¶

Not only the frequencies in the input filter reduces the quality of the signal. The standard frequency in the european power grid has an influence on an analog signal. To weaken this frequency interference signal, another low pass filter is used with a cutoff frequency of 15Hz.

Additionally to this filter, an operational amplifier used as an integrator and amplifier with a gain of 1.2 is inserted to smooth and amplify the signal.

To show the effect of that filter, , with a jumper can chosen between the filtered signal and the output of the thermocouple amplifier.

Charge bucket¶

The charge bucket, built like a low pass filter, is used for the ADC to hold the signal stable while the ADC reads the current voltage level.

Analog Digital Converter thermocouple expansion board¶

The ADC LTC2360 on the thermocouple expansion board can as the digital option be read with SPI. The resolution from the ADC is 12-bit. The input can be enabled or disabled by setting the solderbridge.

Analog Digital Converter nucleo-f446re¶

The ADC on the nucleo-f446re board can be read directly with the internal hardware registers. The nucleo has 3 ADC included. As the external ADC on the thermocouple board, the internals ADCs have 12-Bit. For more informations about the ADC see in the reference manual section 13.