How to detect the platinum rhodium content of a thermocouple?

For S-scale thermocouple platinum rhodium alloy wire, rhodium contains 10%; For the platinum rhodium alloy wire of R scale thermocouple, rhodium contains 13%; For B-grade thermocouple platinum rhodium alloy wire, the positive wire contains 30% rhodium and the negative wire contains 6% rhodium.

Take a cup of engine oil, try to heat it up, insert a glass tube mercury thermometer (200 ℃), heat the oil and keep it at 200 ℃. Insert the end of the thermocouple being tested into the oil and set a four-and-a-half-digit digital multimeter to the DC millivolt range (of course, using a high-precision millivolt meter is better).

1. The reading measured by the digital multimeter is 1.441 millivolts, which is the platinum rhodium alloy wire (positive electrode) in contact with the red probe of the S-scale thermocouple, containing 10% rhodium.

2. The reading measured by the digital multimeter is 1.469 millivolts, which is the platinum rhodium alloy wire (positive electrode) in contact with the R scale thermocouple and the red probe, containing 13% rhodium.

3. The reading measured by the digital multimeter is 0.178 millivolts, which is the B scale thermocouple. The platinum rhodium alloy wire (positive electrode) in contact with the red probe contains 30% rhodium, and the platinum rhodium alloy wire (negative electrode) in contact with the black probe contains 6% rhodium.

Of course, the oil temperature can be raised to 300 ℃, and the S and R calibration thermocouples can better distinguish.

1. The reading measured by the digital multimeter is 2.323 millivolts, which is the platinum rhodium alloy wire in contact with the red probe of the S-scale thermocouple, containing 10% rhodium.

2. The reading measured by the digital multimeter is 2.401 millivolts, which is the platinum rhodium alloy wire in contact with the R scale thermocouple and the red probe, containing 13% rhodium.

3. The reading measured by the digital multimeter is 0.431 millivolts, which is the B scale thermocouple. The platinum rhodium alloy wire (positive electrode) in contact with the red probe contains 30% rhodium, and the platinum rhodium alloy wire (negative electrode) in contact with the black probe contains 6% rhodium.