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Choosing a chart recorder.

Chart recorders provide continuous, real-time, permanent graphic records (paper traces) of DC voltage input signals. Permanent, unalterable graphic recordings of the data from various equipment are required for validation of the data and/or process by regulatory bodies like the EPA and the FDA.

Applications for chart recorders include: chromatography lab documentation; aerospace, automotive, electric, semiconductor, and wire manufacturing industry monitoring; furnace performance validation; environmental monitoring; water and waste water control; medical measurements; and temperature/humidity climate control monitoring.

In choosing the appropriate chart recorder for a given application, you need to consider the following basic selection criteria:

* chart configuration

* chart size

* input type

* number of pens/channels

* chart speeds, and

* special options/features

Chart configuration types include flatbed, vertical-face, and circular recorders. Flatbed strip chart recorders are considered to be general purpose recorders. They can be used for all of the applications referenced in this article, plus many more. They allow easy annotation and ready reference of the recorded data, particularly in chromatography applications.

Vertical-face recorders are used primarily in environmental and industrial process monitoring applications, most of which are typically performed in harsh environments (e.g., dusty and humid). These recorders protect the recorded data by taking up the chart paper on an interior paper spool enclosed behind a protective door.

Temperature/humidity climate control monitoring applications typically employ circular chart recorders, which allow quick visual inspection of up to 31 days of temperature/humidity measurements on one circular sheet of chart paper.

Chart sizes on flatbed and vertical-face recorders typically range from compact, 100-mm wide charts to large, 250-mm wide charts. In choosing a chart size for a flatbed or vertical-face recorder, you need to consider the range of the input being recorded and the amount of available bench or rack space.

Circular charts range in size from 10.2 cm to 25.4 cm dia depending on the number of divisions you need in a given measuring range of temperature and humidity values. Circular chart recorders are typically equipped with wall mounting hardware.

Input type is a critical consideration in choosing a chart recorder. If your application requires the recording of millivolt or volt signals, a flatbed or vertical-face recorder with a standard input range of 1 mV to 5 V, including 10 selectable voltages within this range, would be a good choice. Some flatbed and vertical face recorders are equipped to handle inputs of up to 50 V.

If your applications are more demanding than this and require that you record electrical current, temperature, pH, pressure, strain, or voltage signals, you should consider using a recorder that employs module-based signal conditioning input.

Flatbed and vertical face recorders with removable signal conditioning modules give you the flexibility to quickly and easily change the input signal of your recorder depending on your application needs. These modules accommodate various types of thermocouples, gauges and sensors. Circular, temperature/humidity chart recorders generally come with a thermocouple and humidity sensor.

The number of pens/channels on a chart recorder defines the number of input signals that can be simultaneously recorded. Flatbed and vertical-face chart recorders typically have the capacity to record up to four input signals. Circular, temperature/humidity chart recorders usually accommodate only two input signals.

Chart speeds for flatbed and vertical-face recorders typically range from 1 cm/hr to 30 cm/min with up to 22 selectable chart speeds. Recorders with a range of 0.5 cm/hr to 10 cm/min are also available.

The time span of your application and the relative frequency at which the input signal changes will help you determine which recorder is appropriate for your needs. Circular, temperature/humidity recorder chart speeds are determined by the time or day interval for which recordings are needed.

Special options/features available on flatbed and vertical face recorders are designed to meet specific application needs. For example, environmental monitoring applications and waste water industries often require field-compatible, portable, battery-powered, vertical face chart recorders or chart recorders housed in NEMA 13 sealed weatherproof cases.
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Author:Studt, Tim
Publication:R & D
Date:May 1, 1998
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