The Sentinel range of microprocessor-based circular chart recorders is available in 1, 2 or 3 channel versions. Each channel is equipped with a universal signal input which is compatible with all industry standard sensors and signals including thermocouple types J, K, T, E, N, R, S and B, PT100 platinum resistance temperature detectors and 4/2OmA current loops. Low and high measurement ranges are provided for each input type, separate range cards are not required. Multipen versions include opto-electronic isolation of the input stages to eliminate troublesome installation ground loops.

Precise measurements are assured by the use of multi-slope integrating analogue-to-digital converters with 16-bit resolution which sample the input every 0.5 seconds. Thermocouple and RTD characteristics are fully linearized by means of software. In addition, thermocouple measurements benefit from automatic cold-junction compensation which uses software correction in conjunction with a stable platinum resistance detector for cold-junction temperature sensing.

Alarm relay facilities are comprehensive. Single pen recorders are equipped with three failsafe single-pole changeover relays, six relays are standard on the two and three pen versions. Color-coded light-emitting diodes show the status of each relay at a glance. All relay functions are under software control: set point values and hysteresis levels are entered directly via the keypad, relay action and channel assignment are selected from user-friendly menus. Relays may be freely assigned to any recording channel.

Circuit precision is matched by the unique backlash-free pen drive mechanism which provides positioning resolution better than 0.1%. An integral feedback potentiometer enables closed-loop monitoring of each pen position. Low-maintenance stepper motors are used throughout.

The rotation speed of the 244mm diameter chart is microprocessor-controlled and user programmable. Linear Sentinel charts are compatible with other recorders in the Rototherm range. All Sentinel recorders are housed in a strong molded case that can be panel or surface mounted. A gasketed lockable door protects internal components from harsh industrial environments and offers protection generally to IP55. A tough acrylic window allows the chart trace, digital channel readings and alarm status to be viewed with the recorder's door closed.

Ease-of-operation is an important feature of all Sentinel recorders. The operator's panel includes a five position tactile keypad and a two-line backlit liquid crystal display with large easy-to-read characters. Using this straightforward interface the Sentinel is quickly configured to suit each application. Clear prompts and menus presented on the large character display guide the operator through the setup procedure with confidence.

The input type, chart range, display units, chart speed and relay configurations are selected from logically- ordered option menus. At each stage of the setup procedure the display recalls the value or setting currently stored memory and data entries are checked automatically. The keypad allows direct entry of numerical values such as relay setpoints and measurement ranges. The time for a chart revolution may be set between 1 hour and 31 days in steps of 1 hour or 1 day.

Equally comprehensive user-friendly software is built-in for trouble-free calibration.To ease chart changing a motorized pen lifter parks the pens at the edge of the paper. Sentinel's high speed chart advance / reverse facility allows the chart to be set quickly to the correct time mark.

Three levels of security, including password and hardware protection are available to stop unauthorized access and alteration of the recorder's configuration. All configured data (type of input, chart range, chart speed, display units, setpoints, etc.) are stored in nonvolatile memory for security in the event of power failure.

Each Sentinel is fully calibrated during manufacture and may be pre-configured if required.

SIMPLE TO INSTALL AND MAINTAIN

A choice of mounting options enables simple installation in a panel or surface mounting on a wall. The Sentinel recorder case is compatible with the standard Rototherm recorder panel cutout.

Sentinel's closed-loop feedback mechanism and circuits with excellent long-term stability maintain performance and keep recalibration to a minimum, cutting the costs of maintenance.

The Sentinel is designed, manufactured and tested to BS EN ISO 9001. Each Sentinel recorder carries Rototherm's 12 month warranty.