Athena 2000 Series Manuale operativo - Pagina 7

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Thermocouple

Placement

Proper thermocouple placement can eliminate many problems in the system. The probe should be placed

so that it can detect any temperature change with little thermal lag. In a process that requires fairly constant

heat output, the probe should be placed close to the heater. In processes where the heat demand is

variable, the probe should be close to the work area. Some experimenting with probe location can often

provide optimum results.

In a bath process, the addition of a stirrer will help to eliminate lags. Since the thermocouple is basically a

point measuring device, putting more than one thermocouple in parallel will provide an average temperature

reading and produce better results in air-heated processes.

Operation

The typical control system contains the sensor, controller and the process (load). The sensor produces

a small signal proportional to the measured temperature of the process. This signal is amplified by the

controller, where it is compared with setpoint temperature. If the temperature of the sensor is below setpoint,

the output circuitry will be actuated to apply power to the process. This is indicated by means of an LED light

in the lower center of the front panel. The deviation meter will swing to the extreme left. It will remain there

until the temperature of the probe rises to within 50 °F of setpoint, and then will continue to rise to the null

point (zero degree deviation). The deviation meter accurately displays the difference between the probe's

(process) temperature and the desired setpoint temperature.

-B - Relay Output

The "B" output is a relay rated at 7 A, 120 Vac and 5 A, 240 Vac. These contacts can be wired to provide

power to a heater within the above rating. A contactor can be operated to handle a larger load. Solenoids

can be operated to control oil or gas heaters.

The controller operates as a narrow band controller when the band adjustment is set at the narrow position.

As the band is widened, the unit becomes a time-proportioning controller, which provides close temperature

control. The percentage of the time when the relay is energized is varied by the controller to meet the load

requirements.

NOTE:

screws.

Maximum cycle time setting is 15 seconds.

-F - Current Output

Current proportional output of the -F unit is a 4 to 20 mAdc signal into 1000 ohm maximum. This output can

be used to drive power controllers, motor positioners or electropneumatic actuators.

-S - Pulsed Voltage Output

This output is similar to the -F output with the exception of a pulsed time base rather than a fully proportional

current output signal. This output is designed to drive solid state contactors.

-L - Limit Control Output

The -L output unit is designed as a high limit controller and is a variation of the -B output controller. The

time proportioning circuit, along with the proportional band and offset (manual reset) adjustments, have

been eliminated. A reset pushbutton has been added to the front panel and extends beyond the door.

When power is applied, the controller will energize except for the output relay, which will operate after the

reset button is pushed. The green LED indicates the safe or non-alarm condition. When the measured

temperature exceeds the setpoint, the relay will de-energize and the green LED will turn off.

Lights or horns can be driven directly, because the SPDT relay contacts are rated 7 A at 120 Vac or 5 A at

240 Vac.

-T - Solid State Output

The -T output unit has a solid state relay with SPST contacts rated at 1 A, 120/240 Vac (10 A inrush

maximum). These contacts can be wired to provide power to a heater within the above ratings, and a

contactor can be added to handle larger loads. Solenoids can be operated to control oil or gas heaters.

To reach the plug-in module, push reset button while opening the door, and then remove two (2)