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Chart Recorders & Charts

When a health inspector, a quality auditor, or a customer asks whether that walk-in held temperature over the weekend, a circular chart answers the question in one glance. Chart recorders have been the standard for documenting refrigeration temperatures for decades because they work without a computer, a network, or a login. Clip on a chart, set the time, and the recorder draws a continuous trace that anyone can read and file.

This category covers Supco circular chart recorders, including the CR87 series for temperature and pressure, along with the replacement charts and supplies that keep them running. Charts are available in common rotation periods, including 6-hour, 24-hour, 7-day, and 31-day, so you can match the level of detail to how the record will be used.

Restaurants and commercial kitchens use chart recorders on coolers and freezers as part of a HACCP plan. Refrigeration contractors use them as a diagnostic tool, leaving one on a case or walk-in to catch defrost problems, door-left-open events, or a compressor that short-cycles overnight. Labs, florists, pharmacies, and warehouses use them where a paper trail is required or simply preferred.

How a Circular Chart Recorder Works

A circular chart recorder has three basic parts: a clock-driven chart plate, a sensing element, and a pen arm. The chart turns at a fixed rate, one full revolution per rotation period, while the pen moves in and out across the chart's radius as the measured value changes. The result is a continuous line plotted against time.

  • Temperature recorders use a sensor, either built in or on a remote probe, to read air or product temperature. A remote probe lets the recorder mount outside the box while the sensor sits inside the cooler or freezer.
  • Pressure recorders connect to a system or line and plot pressure over time, which is useful for spotting cycling patterns or pressure drift.
  • Charts are printed with a specific scale range and time grid. The chart must match the recorder's range and rotation, or the trace will be meaningless.
  • Pens are consumable. A dry or clogged pen leaves gaps, so keep spares on hand.

Because the trace is continuous, a chart shows more than a spot reading ever could: how long defrost lasted, how fast the box recovered, whether temperature spiked during a delivery, and whether the system held steady through the night.

When to Replace Charts, Pens, or the Recorder

  • Every rotation. Change the chart at the end of each rotation period: daily for a 24-hour chart, weekly for a 7-day chart, monthly for a 31-day chart. Date it, initial it, and file it.
  • Faint, skipping, or blotted lines mean the pen is drying out or the pen arm is not making even contact.
  • A trace that does not match a reference thermometer. If the recorder disagrees with a known-good thermometer, check calibration per the manufacturer's instructions.
  • Charts that do not line up with the clock. If the time on the chart drifts, check the batteries or power supply and the chart drive.
  • A flat line that never moves, even through defrost or door openings, can point to a failed sensor, a damaged capillary or probe lead, or a stalled chart drive.
  • Physical damage, such as a cracked door, broken pen arm, or moisture inside the case, especially on units mounted in wet or washdown areas.

How to Choose the Right Recorder and Charts

Pick the rotation for the job

Shorter rotations spread time across more of the chart, so you see more detail. Longer rotations compress time but require fewer chart changes.

  • 6-hour charts are diagnostic. Use them when you need to see individual compressor cycles, defrost terminations, or short events.
  • 24-hour charts are a good balance for daily food safety logs and troubleshooting overnight issues.
  • 7-day charts are the common choice for routine cooler and freezer records, with one change per week.
  • 31-day charts suit stable applications where monthly records are enough.

Match the chart to the recorder

Charts are model-specific. Confirm the recorder model, the chart diameter, the temperature or pressure range, and the rotation before ordering. A chart with the wrong range will plot the pen in the wrong place, and a chart with the wrong rotation will misstate time. The product pages list compatible recorder models.

Match the range to the application

A freezer chart needs a range that covers well below 0°F. A cooler chart should cover the normal holding range plus enough headroom to show a failure. Pick a range that keeps the normal operating line away from the chart edges.

Think about mounting and power

Decide where the recorder will live, whether a remote probe is needed, and how it will be powered. Mount it where staff will see it and change the chart on schedule.

Chart rotation Change frequency Detail level Best for
6-hour Every 6 hours Highest Diagnosing cycling, defrost, and short events
24-hour Daily High Daily food safety logs, overnight troubleshooting
7-day Weekly Moderate Routine cooler and freezer records
31-day Monthly Lower Stable storage with monthly documentation

Installation and Usage Tips

  • Place the probe where it represents the product. Avoid putting the sensor directly in the evaporator discharge air, next to the door, or against a wall. A center-of-box location, or a product-simulating probe if your plan calls for one, gives a truer reading.
  • Route probe leads carefully. Do not pinch leads in a door gasket. Use an existing penetration or seal any new one so you do not create a frost or condensation problem.
  • Set the time correctly. Line up the current time on the chart with the time index on the recorder when installing each chart. A chart set 12 hours off makes a perfect record useless.
  • Verify against a reference. Check the recorder against a calibrated thermometer when you install it and periodically after. Note the check on the chart or in your log.
  • Write on every chart. Record the unit, location, start date and time, and initials. Note anything unusual, such as a delivery, power outage, or service visit.
  • Keep spare pens and charts nearby. A gap in the record is often what draws attention in an audit.
  • Pressure recorder connections on a refrigeration system should be made by a qualified technician. Opening a refrigerant circuit requires EPA 608 certification.

Charts and HACCP Records

A HACCP plan identifies critical control points and requires monitoring and records to prove they stayed in limits. For refrigerated storage, temperature is the critical limit, and a chart recorder provides continuous monitoring with a dated, initialed record. Check your local health department and your own HACCP plan for the exact requirements, including how long records must be kept. Many operations use the FDA Food Code cold-holding limit of 41°F or below for cooler storage, but your plan and local rules govern.

Part Details & Shipping

Supco has built test and monitoring instruments for the refrigeration trade since 1945, and its chart recorders and charts are a familiar sight in commercial kitchens and on service trucks. HVAC365 lists compatible models and specs on each product page, with spec sheets where available, so you can match charts to your recorder before ordering. Charts and recorders ship in 3-5 business days, so you can reorder before you run through your last pack.

Frequently Asked Questions

Can I use a 7-day chart on a 24-hour recorder?

No. The chart drive turns at a fixed rate set by the recorder. A chart with a different rotation will misstate time. Use only charts that match the recorder model and its rotation, unless the recorder is designed with a selectable rotation.

Which rotation is best for troubleshooting a walk-in?

A 6-hour or 24-hour chart gives you enough detail to see compressor cycles, defrost periods, and recovery times. Once the problem is solved, switch back to a 7-day chart for routine records.

How do I know the recorder is accurate?

Compare it to a calibrated reference thermometer at the probe location. If it reads off, follow the recorder's calibration procedure. Record each check so you have proof of verification.

Are chart recorders accepted for HACCP?

Chart recorders are widely used for HACCP temperature monitoring because they provide a continuous, dated record. Your local health department and HACCP plan set the specific requirements, so confirm with them.

Should I switch to a data logger instead?

Data loggers store readings digitally and are easier to archive and analyze on a computer. Chart recorders give a visible, instant record without software. Many operations use both: a chart on the door for staff and inspectors, and a logger for long-term data.

What causes gaps in the chart line?

The most common causes are a dry pen, a pen arm that is not touching the chart evenly, or a stalled chart drive from weak batteries or a power interruption. Replace the pen first, then check power and the drive.

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