August, 2007

With pen recorders, pen offset (phase differences) between pens along the time axis are inevitable when measurement data is recorded on chart paper. Phase differences are one of the factors that prevent the accurate plotting line of measurement data.
This article explains the principles and working of the pen offset compensation function, which is included in the Pen Recorder µR10000 and µR20000 series, and corrects pen offsets.

On 2-pen, 3-pen, and 4-pen recorders, the alignment of each pen causes difference in the mechanical positions of the pens. Therefore, there are offsets along the time axis (phase difference) between the pens. If pen offset compensation is enabled, all pens are aligned with the reference pen and plotted.

Below is an explanation for the 4-pen model. (The principles also apply to 2-pen and 3-pen recorders.)
The figure 1 below shows from the side how a 4-pen recorder plots measurement data on chart paper.

The figure 1 above shows the offsets between the pens. Specifically, the offset of the 1st pen is equivalent to a length P1, that of the 2nd pen is equivalent to a length P2, and that of the 3rd pen is equivalent to a length P3. Because of these offsets, measurement data acquired at the same time cannot be recorded in the same position on chart paper. (See the figure 2 "Normal Recording" below.)

If, however, pen offset compensation is enabled, measurement data equivalent to the offset of each pen (other than the reference pen) is recorded to memory, and recording (plotting) starts at the point in time when chart paper is fed at a length equivalent to the offset for each pen. As a result, offsets can be corrected when measurement data is recorded on chart paper. (See the figure 3 "Pen Offset Compensation Recording" below.)

Even if the chart speed is changed during the pen offset recording mode, the measurement data after the change is made is normally recorded at the changed chart speed. Furthermore, even if interruptions such as alarm printout or message printout occur, printout is not disrupted by the pen offset, so the printed content can be confirmed quickly.

Reference:
The µR1000 and µR10000 Recorder User's Manual, Yokogawa Electric Corporation