Barrettor vs. Thermistor: Understanding the Key Differences

Power measurements at microwave frequencies often rely on thermally sensitive devices. These devices leverage the heat generated by microwave energy when electromagnetic waves interact with them.

This article outlines the differences between barrettors and thermistors, both used for power measurement in microwave applications.

Thermistor

Thermistor

A thermistor is essentially a small semiconductor bead with connecting wires, as illustrated above. Its resistance decreases as temperature increases. The bead material is typically a mixture of manganese and nickel oxides combined with copper dust.

Barrettor

Barrettor

A barrettor, in contrast, is a short, fine wire, usually made of platinum with a silver coating. Its resistance increases with temperature.

Key Differences

Here’s a breakdown of the key differences between barrettors and thermistors:

• Thermal Time Constant: Barrettors have a low thermal time constant (typically 100 to 300 µs), while thermistors have a larger time constant.
• Operating Temperature: Barrettors operate at high temperatures. Because of this, changes in ambient temperature don’t significantly affect their operation. Thermistors operate at lower temperatures, making them more sensitive to ambient temperature fluctuations.
• Broadband Suitability: Barrettors are generally not suitable for broadband systems.
• Detector Sensitivity: Barrettors exhibit poor detector sensitivity (around 5.2 Ohm/mWatt), while thermistors offer high detector sensitivity (around 60 Ohm/mWatt). This makes thermistors more suitable for low-power measurements.

In summary, thermistors are generally preferred for low-power measurements due to their higher sensitivity, while barrettors, although less sensitive and not suitable for broadband, offer a faster response time.