Diagnostic LEDs
The G168 is equipped with three front panel LEDs. The dual function green LED is labeled INPUT and 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 the wiring connection. If the input signal is more than 110% of the full scale range, the LED will flash at 8 Hz. Below 0%, it flashes at 4 Hz. Two red LEDs indicate the relay state for each setpoint. An illuminated red LED indicates the tripped condition.

Output
The G168 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 G168 limit alarm setpoints can be configured for HI or LO, failsafe or nonfailsafe operation. Each of the setpoints have 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 LO 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
Circuitry in the G168 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 results in a “dynamic deadband” (based on time) in addition to the normal deadband.

Configuration
Unless otherwise specified, the factory presets the Model G168 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 to reconfigure switches SW1 and SW2 for the desired input type, range and function.

• With DC power off, position input switch "SW1-9, 10" for voltage or current.
• Set position 1 through 8 of “SW1” for the desired input range
• Set position 1 and 2 of "SW2" to ON for a HI trip setpoint or OFF for a LO trip
• Set position 4 of "SW2" to ON for nonfailsafe operation or OFF for failsafe operation (e.g., alarm trips when power fails).

Calibration
Note: To maximize thermal stability, final calibration should be performed in the operation installation, allowing approximately 1 to 2 hours for warm up and thermal equilibrium of the system.

1. After configuring the dip switches, connect the input to a calibrated AC source and apply power.
2. Setpoint: set deadband at its minimum (fully counterclockwise) before adjusting the setpoint. With the desired trip input applied, adjust the setpoint until the relay trips. For HI trip calibration, start with the setpoint above the desired trip (fully clockwise). For LO trip calibration, start below the desired trip (fully counterclockwise).
3. Deadband: Set deadband to its minimum (fully counterclockwise). Set the setpoint to the desired trip. Adjust the input until the relay trips. Readjust deadband to 5% (fully clockwise). Set the input signal to the desired deadband position. Slowly adjust deadband until the relay untrips

Relay Protection & EMI Suppression
When switching inductive loads, maximum relay life and transient EMI suppression is achieved using external protection (see Figures 2 and 3). Place all protection devices directly across the load and minimize all lead lengths. For AC inductive loads, place a properly rated MOV across the load in parallel with a series RC snubber. Use a 0.01 to 0.1uF pulse film capacitor (foil polypropylene recommended) of sufficient voltage, and a 47 ohm, 1/2W carbon resistor. For DC inductive loads, place a diode across the load (PRV > DC supply, 1N4006 recommended) with (+) to cathode and (-) to anode (the RC snubber is an optional enhancement).