Recorders are data acquisition tools used to monitor systems and processes by recording data points over a timed interval. A recorder is the perfect device for those situations where it is prudent or necessary to document conditions, verify that systems are working properly, or to comply with regulatory requirements. Since recorders produce a permanent archive of conditions, either as a hardcopy or within a digital memory, the data can be stored indefinitely and used for future reference.
Recorders use data acquired from sensors to generate a plot, graph, or another visualization of the data over a timed interval. Common applications for recorders include temperature and humidity measurements, flow rates, pH, pressure, as well as a host of other process measurements. 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.
Though recorders are similar to data loggers as both are data acquisition tools, each is best suited for different roles. Recorders excel in applications where instant visual feedback is preferred while data loggers are best used for applications where the device is meant to be left unattended for a period of time. You can read more about data loggers on the description page for that category.
There are three basic types of recorders available:
Circular chart recorders archive data points on a round chart that rotates uniformly. 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.
Strip chart recorders use a long roll or strip of paper that passes at a uniform speed beneath one or more pens. The data is plotted onto the chart in proportion to the signal received. Strip chart recorders are especially well suited for recording continuous processes. The benefits of strip chart recorders includes the ease of operation, the hardcopy it produces, and real-time output.
Videographic recorders use a graphic display rather than paper charts to record data. The data is stored in a digital format which can be viewed in real-time or recalled later. Data can also be transferred to computers for archiving or generating reports. Benefits of paperless recorders include better programming options, no need for charts and pens, and the ability to more easily handle large amounts of data. Scaling and mathematical functions are also possible.
Circular and strip chart recorders require the correct charts and pens to work correctly.
Recorder Technology
Generally speaking, 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 chart paper (for chart or strip recorders) is 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 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 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.
