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| resources:eval:user-guides:eval-ad7441x:tools:thermocouple [25 Jun 2021 18:08] – Description Update Bríde Ní Riagáin | resources:eval:user-guides:eval-ad7441x:tools:thermocouple [14 Sep 2021 16:11] (current) – updated link back to TOC Bríde Ní Riagáin | ||
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| - | =====Thermocouple & Cold Junction Compensation Measurements with AD74412R/AD74413R===== | + | =====Thermocouple & Cold Junction Compensation Measurements with AD74413R===== |
| - | ~~NOTOC~~ | + | |
| ====Introduction==== | ====Introduction==== | ||
| - | The AD74413R is a quad channel software configurable I/O IC solution | + | The AD74413R is a quad channel software configurable I/O IC that provides multiple analog and digital functions to a single pair of screw terminals. The AD74413R is configured over a single SPI interface. The part offers Voltage/ |
| \\ Refer to figure 1 for a high level block diagram of the required connections for thermocouple measurements. | \\ Refer to figure 1 for a high level block diagram of the required connections for thermocouple measurements. | ||
| - | \\ The thermocouple should be connected between the I/OP and I/ON screw terminals. The AD74413R can be configured in Voltage Input mode, with the ADC range set to the ±104mV range to measure | + | \\ |
| + | \\ The thermocouple generates a voltage that is proportional to the temperature difference between the measurement point and where the thermocouple is connected at the screw terminals, the cold junction. | ||
| + | To be able to determine the temperature at the measurement point, the cold junction temperature must be measured along with the voltage generated by the thermocouple. | ||
| + | \\ The thermocouple should be connected between the I/OP and I/ON screw terminals. The AD74413R can be configured in Voltage Input mode, with the ADC range set to the ±104.16mV | ||
| \\ The AD74413R can support cold junction compensation measurements by measuring the response from an external thermistor resistor divider using the onboard diagnostics. The LVIN pin can be used to measure the thermistor voltage within an ADC range of 2.5V. The resistor divider can be placed close to the terminal pins where the thermocouple is connected. | \\ The AD74413R can support cold junction compensation measurements by measuring the response from an external thermistor resistor divider using the onboard diagnostics. The LVIN pin can be used to measure the thermistor voltage within an ADC range of 2.5V. The resistor divider can be placed close to the terminal pins where the thermocouple is connected. | ||
| - | \\ The temperature at the Thermocouple | + | \\ The temperature at the thermocouple |
| {{ Thermocouple config.png }} | {{ Thermocouple config.png }} | ||
| - | \\ Figure 1: AD7441xR | + | \\ Figure 1: AD74413R |
| \\ | \\ | ||
| \\ | \\ | ||
| ====Implementation==== | ====Implementation==== | ||
| - | Two measurement steps are taken to determine the temperature of the Thermocouple hot junction. | + | Two measurement steps are taken to determine the temperature of the measurement point. |
| \\ First, the cold junction temperature is measured to establish a reference point for the thermocouple. | \\ First, the cold junction temperature is measured to establish a reference point for the thermocouple. | ||
| - | Figure 2 shows a snapshot from the AD74413R evaluation board. This circuit shows the implementation required to use the AD74413R to determine T< | + | Figure 2 shows a snapshot from the AD74413R evaluation board. This circuit shows the implementation required to use the AD74413R to determine T< |
| - | *The reference to the AD74413R is applied to the top of a resistor divider. The resistor divider is made up of a 33kΩ resistor, R64 and a 33kΩ thermistor, RT1. | + | *The reference |
| *The resistance of the thermistor is proportional to the ambient temperature. The resultant voltage is measured from the tap-off point in the middle of the divider, which is connected to the LVIN pin. The LVIN pin can be measured by the ADC in a 2.5V range, which is set by the reference provided. | *The resistance of the thermistor is proportional to the ambient temperature. The resultant voltage is measured from the tap-off point in the middle of the divider, which is connected to the LVIN pin. The LVIN pin can be measured by the ADC in a 2.5V range, which is set by the reference provided. | ||
| *The resistance of the thermistor can be calculated from the measured ADC_CODE, using the following equation: | *The resistance of the thermistor can be calculated from the measured ADC_CODE, using the following equation: | ||
| Line 23: | Line 27: | ||
| {{ thermocouple sch snapshot.png }} | {{ thermocouple sch snapshot.png }} | ||
| - | + | \\ Figure 2: LVIN schematic configuration | |
| - | The voltage generated by the thermocouple must also be measured. | + | \\ |
| - | \\ Configure one of the AD74413R channels in Voltage input mode with the ADC range set to ±104.16mV. Connect the thermocouple | + | \\ The voltage generated by the thermocouple must also be measured. |
| + | \\ Configure one of the AD74413R channels in Voltage input mode with the ADC range set to ±104.16mV. Connect the thermocouple | ||
| \\ | \\ | ||
| - | \\ V< | + | \\ V< |
| \\ | \\ | ||
| \\ Where: | \\ Where: | ||
| Line 62: | Line 67: | ||
| To enable the 200kΩ to ground, set bit 2 in the ADC_CONFIG register (address 0x05 for channel A). | To enable the 200kΩ to ground, set bit 2 in the ADC_CONFIG register (address 0x05 for channel A). | ||
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resources/eval/user-guides/eval-ad7441x/tools/thermocouple.1624637323.txt.gz · Last modified: 25 Jun 2021 18:08 by Bríde Ní Riagáin