Valley Hold

“Valley hold” is a crucial feature in temperature sensors like bolometers or pyrometers, enabling them to process measured data effectively at a low level. In Optris temperature sensors, valley hold refers to the ability to retain the lowest measured value over a specified period, called the “holding time,” and deliver this value as “TProc” to the sensor’s output. When enabled, the sensor continuously records temperature values and maintains the lowest temperature value detected. If the temperature rises above the lowest detected value, the holding time countdown begins.

Once this time expires, the TProc value gradually approaches the current temperature with increasing step sizes until it either matches the current value or the temperature drops again, prompting TProc to follow as long as it drops. Additionally, there is an advanced valley hold mode available. In this mode, similar to valley hold, the TProc output follows the decreasing amplitude of the measured temperature to maintain its lowest value recorded so far. If the temperature increases, the lowest value measured is retained. To reset the measured lowest value, the temperature must follow a nonlinear curve characterized by rising above a predefined threshold value, then dropping again until it falls below this threshold, and finally rising again by the amount of the user-defined hysteresis.

This process causes a reset of the TProc output to the last measured minimum, which is then maintained as the lowest temperature until the current value drops again and falls below the previous lowest value, prompting TProc to update accordingly. Another reset will occur if the temperature follows the described nonlinear curve again.