Diagnostic LEDs
The G108 is equipped with three front panel LEDs. The green LED is a dual function LED labeled INPUT. This LED indicates line power and input signal status. Active DC power is indicated by an illuminated LED. If this LED is off, check DC power and wiring connection. If the input signal is more than 110% of the full scale range, the LED will flash at 8 Hz. Below 0%, the flash rate is 4 Hz.

Two red LEDs indicate the relay state for each setpoint. An illuminated red LED indicates the tripped condition.

Output
The G108 is equipped with two SPDT (form C) relays, rated at 120VAC or 28VDC at 5 amperes. Each of these relays is independently controlled by the field configurable setpoint and deadband.

Operation
The field configurable G108 limit alarm setpoints can be configured for HI or LO, failsafe or non-failsafe operation. Each of the setpoints has a respective HI or LO deadband. In a tripped condition, the setpoint is exceeded and the appropriate red LED will illuminate. The trip will reset only when the process falls below the HI deadband or rises above the low deadband (see Figure 1). For proper deadband operation, the HI setpoint must always be set above the LO setpoint. In failsafe operation, the relay is energized when the process is below the HI setpoint or above the LO setpoint (opposite for non-failsafe). In the failsafe mode, a power failure results in an alarm state output.

Dynamic Deadband
LSI circuitry in the G108 prevents false trips by repeatedly sampling the input. The input must remain beyond the setpoint for 100 milliseconds, uninterrupted, to qualify as a valid trip condition. Likewise, the input must fall outside the deadband and remain there for 100 milliseconds to return the alarm to an untripped condition. This effectively results in a “dynamic deadband” —based on time— in addition to the normal deadband.

Configuration
Unless otherwise specified, the factory presets the Model G108 as follows:

The DC power input accepts any DC source between 9 and 30V, typically a 12V or 24VDC source is used (see Accessories).

For other I/O ranges, refer to Table 1 and Figure 4. Reconfigure switch SW1 for the desired input type, range and function.

1. With DC power off, set position 9 and 10 of SW1 for current or voltage (see Table 1).
2. Set position 1 through position 4 of input range switch “SW1” for the desired input range (see Table 1).
3. Set position 5 of input range switch “SW1” to ON for unipolar (e.g. zero based, 0-20mA) range or OFF for bipolar (e.g. -100% offset, -20 to 20mA) range (see Figure 4).
4. Set position 6 and 7 of input range switch “SW1” to ON for a HI trip setpoint or OFF for a LO trip setpoint (see Figure 4).
5. Set position 8 of input range switch “SW1” to ON for non-failsafe operation or OFF for failsafe operation (e.g. alarm trips upon power failure).

1. After configuring the DIP switches, connect the input to a calibrated DC source and apply power. Refer to the terminal wiring (Figure 7).
2. Setpoint: set deadband at its minimum (fully counter clockwise) before adjusting the setpoint. With the desired trip voltage or current input applied, adjust setpoint until the relay trips. For HI trip calibration, start with the setpoint above the desired trip (full clockwise). For LO trip calibration, start below the desired trip (full counter clockwise).
3. Deadband: Set deadband to its minimum (fully counter clockwise). Set the setpoint to desired trip. Adjust voltage/current input until relay trips. Readjust deadband to 5% (fully clockwise). Set voltage/current input signal to desired deadband position. Slowly adjust deadband until relay untrips.