Signal damping - PR-33 - PR-33-AC

PR-33-AC User Guide

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The system provides the possibility to enter signal damping to diminish the influence of process noise. The damping is applied to the CONC value (and thus the output signal).

Figure 1. Effect of damping time on measurement with linear damping

There are three different damping types available in the Sanitary OEM Refractometer:

  • Linear damping
  • Exponential damping
  • Slew rate limit damping

Linear damping is a sliding average, and it is recommended for most cases. The damping time represents the averaging time. For fast damping, use 0–2 s damping, for minimal noise, use a value of 10 s or more.

Exponential damping is a single time constant (one pole) low-pass filter. If this option is chosen, the damping time represents the half-time of the filter. The damping time recommendation is the same as for the linear damping.

With both linear and exponential damping the residual random noise is inversely proportional to the square root of the damping time. In practice, using a damping time of more than 30 seconds does not improve the noise performance. It should also be noted that increasing the damping time will deteriorate the response speed of the instrument.

If the process signal has short erroneous high or low peaks, slew rate limit damping can be used to cut their effects. Slew rate limit damping limits the maximum change for the output signal in one second. Slew rate limit damping is recommended for random noise suppression as it is non-linear.

The slew rate parameter is presented in output units. For example when the concentration is measured in percentages, typical slew rate value is 0.05