Agilent 5991-3196EN Gauging Temperature Accuracy Using the Keysight U3606B Multimeter DC Power Supply- App free download

File name 5991-3196EN Gauging Temperature Accuracy Using the Keysight U3606B Multimeter _ DC Power Supply- App

Keysight Technologies Gauging Temperature Accuracy Using the U3606B Multimeter | DC Power Supply Application Note Introduction Temperature plays an important role in maintaining the overall functionality of an electrical appliance and the design of these controller circuits is getting increasingly stringent. This makes it important to test the integrity of components and the overall the controller circuit. This article illustrates the unique features of the Keysight Technologies, Inc. U3606B multimeter | DC power supply that can be used to evaluate the functionality of a temperature controller board. 03 | Keysight | Gauging Temperature Accuracy Using the U3606B Multimeter | DC Power Supply - Application Note How a Temperature Controller Circuit Works Figure 1. Temperature controllers found on refrigerators Figure 2 illustrates a temperature controller circuit that uses a LM339 comparator. A LM339 chip contains four comparators, but this specific circuit only uses one of them. The operation of the circuit is simple. When the voltage at positive input (pin 5) is higher than negative input (pin 4), the output of LM339 (pin 2) will turn On. The thermistor in this circuit acts as a voltage divider. Its resistance decreases when the temperature drops. This brings more voltage on the positive pin of the LM339. Notice there is also another voltage divider in the circuit which is constructed on a variable resistor and connected to the negative pin of the LM339. In most cases, when the temperature setting on an analog refrigerator is changed, it is actually the variable resistor that is being adjusted. When the output of the LM330 turns On, it turns On the transistor which powers up the thermostat circuit. The thermostat circuit then switches the cooling and heating elements On and Off to maintain the temperature within the correct range. An LED is usually connected to the thermostat circuit to serve as an indicator and it illuminates when the thermostat circuit is turned On. + Thermistor