How to Read a Circular Chart Recorder Chart
A circular chart recorder chart shows a measured process variable over time: the chart paper moves according to the recorder’s time base while a pen marks the measured value. To read it, first identify the chart and its printed scales, then match a point on the trace to both the time and measurement axes.
Quick answer
Start with the chart’s printed model or part number, time interval, units, and scale. Use the chart’s own time marks and measurement graduations to interpret the trace; chart duration, rotation direction, and scale layout can vary by recorder and chart.
1. Identify the chart before interpreting the trace
Check the chart face, label, or accompanying record for the recorder make and model, chart part number, process variable, units, and measurement range. These details tell you which time and value scales apply. A chart that looks similar is not necessarily the correct chart for the instrument.
If the chart has several scales or printed ranges, use the one specified for the recorder and channel being reviewed. When the chart identity or range is unclear, consult the recorder manual or the site procedure instead of estimating.
2. Find the chart’s time base
Look for the time labels and the stated chart duration on the paper or its packaging. Circular charts may be designed for different recording periods, so do not assume that one revolution always represents a particular number of hours or days.
Use the printed time marks to locate the event you want to review. If you know when the chart was installed or changed, use that documented start time to establish the date and time represented by each mark. Confirm the rotation direction from the chart markings or recorder documentation.
3. Match the pen trace to the measurement scale
Find the units and scale for the recorded variable, such as °C, pressure, or another process unit. At the time mark of interest, follow the trace to the corresponding graduation and read the value using the chart’s printed scale.
Some charts use radial graduations and others have a different layout. Read the scale printed on that specific chart rather than assuming that distance from the centre always has the same meaning. Record an approximate reading as approximate; a paper trace is not a substitute for the instrument’s specified calibration or measurement uncertainty.
4. Read multi-channel charts by using the legend
On a recorder with more than one pen, check the chart legend, channel labels, or site record to identify which trace belongs to which variable. Ink colour can help distinguish traces, but colour alone should not be used to identify a process variable unless the chart or procedure confirms the assignment.
When traces overlap, use the chart legend and recorder channel setup to distinguish them. Do not infer a missing trace or assign a trace to a channel based only on its apparent position.
5. Preserve the record and document the context
Follow the site procedure when removing, labeling, reviewing, or storing a chart. Record relevant context such as the instrument tag, chart range, chart-change time, reviewer, and any observed gaps or unusual marks where your recordkeeping process requires it.
A gap, smear, or unexpected jump should be documented and investigated under the applicable procedure. Do not redraw or alter the trace. If the chart, time base, or instrument setup cannot be confirmed, ask the responsible instrument or quality team before relying on a reading.
Frequently Asked Questions
How do I know what time period a circular chart represents?
Check the chart face, chart label, or recorder documentation for the chart duration and time marks. Do not assume every circular chart covers the same number of hours or days.
Do all circular chart recorders rotate in the same direction?
No. Confirm the time direction from the printed chart markings or the manual for that recorder before assigning a time to a trace.
Can I identify a multi-pen trace by colour alone?
Not reliably. Use the chart legend, channel labels, or the recorder’s documented setup to confirm which variable each trace represents.
Can a paper chart confirm that a recorder is calibrated?
A chart shows the recorded trace, but it does not by itself prove calibration status or measurement accuracy. Follow the instrument’s calibration records and the site’s review procedure.
Related Guides
Contact Devki — share the complete recorder model and revision, arm or mount, tip, and ink for a catalog review and quotation-specific terms.