Circular chart recorders archive data points on a round chart over a timed interval. Using data acquired by one or more sensors, circular chart recorders rotate uniformly
while one or more pens plots the data radially in proportion to the signal received. The charts usually rotate over standard time periods (e.g. 24 hours, one week, one month, etc.)
though some recorders can rotate over non-standard lengths of time. The benefits of circular chart recorders includes the ease of operation, the hardcopy it produces, and real-time
output.
Common applications for circular chart recorders include temperature and humidity measurements, flow rates, pH, pressure, as well as a host of other process measurements. Circular
chart recorders are available in single or multichannel styles and in various configurations. Many recorders can also record information in a digital format for download to a computer.
Circular chart recorders require the correct charts and pens to work correctly.
Circular Chart Recorder Technology
Generally speaking, circular chart recorders simply render data. The data itself is produced by application specific sensors that attach to the recorder. Sensor types include temperature
(thermocouple, thermistor, RTD), strain gauge or bridge, current, humidity, level, pressure, pH, as well as many others.
Sensors can be either active or passive devices. Passive sensors, like thermocouples, do not require an outside power supply to generate a signal. Active sensors, on the other hand, do
require a power supply to generate a signal. Power to active sensors is often provided by the recorder and is referred to as the excitation source. Signal excitation can either be a voltage
or current output.
As the recorder receives a digital signal, analog signal or sensor input, the circular charts are driven past the pen (or pens) at a steady rate by the drive mechanism. The pen assemblies
typically use a galvanometer or potentiometer to drive the marking device.
Galvanometric recorders have a light coil of wire magnetically suspended that is deflected by the sensor current. The pen records those fluctuations, effectively transcribing
the sensor current. Sensitivity, however, is limited with galvanometers, particularly with analog instruments. Galvanomteric recorders typically have slow response, small bandwidth, low input
impedance, and low sensitivity.
Potentiometric recorders compare the input signal with a reference which results in an error signal which is amplified thus driving the pen motor. Potentiometric recorders
typically have a fast response , smaller bandwidth, very high input impedance, and high sensitivity.
Some things to Consider When Purchasing Circular Chart Recorders:
- Is a visual record preferred?
- Does monitoring need to be continuous or is sampling sufficient?
- How long will the device be used to record or log?
- Will the device be left unattended?
- Will the device be in a hazardous area?
- How many sensors will be used?
- What level of accuracy is required?
If you have any questions regarding circular chart recorders please don't hesitate to speak with one of our engineers by e-mailing us at sales@instrumart.com or calling 1-800-884-4967.
