Understanding power meter and sensor key specifications is vital for selecting the right equipment for power measurements. An often overlooked area is the DC or AC coupling characteristic of the power sensor. Choosing the wrong type of sensor can result in measurement inaccuracy and — or even worse, damage to the power sensor. This article compares the DC-coupled sensors to AC-coupled ones (also known as «DC-blocked» sensors). Several application examples are included to illustrate the key differences. The article concludes with choices of both DC-coupled and DC-blocked sensors from Agilent Technologies to suit the user’s application requirements.