Diagnostic LEDs
The Q126 is equipped with three front panel LEDs. The first is a dual function LED labeled IN (INPUT) This green LED indicates AC power and input signal status. Active AC power is indicated by an Protecting the Integrity of Industrial Process Signals An Invensys Company illuminated LED. If this LED is off, check line power and wiring connection. If the input signal is 7% above or below the configured input range the green LED will flash at 8Hz or 4Hz, repectively.

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

Output
The Q126 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 Q126 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.

Dynamic Deadband
LSI circuitry in the Q126 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 Q126 as follows:

For other I/O ranges, refer to Table 1 and reconfigure switches SW1 and SW2 for the desired input type, range and function.

1. With the module removed from the rail and not powered, snap off the faceplate by lifting the right edge away from the heat sink. Note the input switches (SW1 & SW2) are located under the face plate. Set positions 1 through 3 on "SW1" and positions 1 through 8 on "SW2" for the desired input and range. (see Table 1)
2. Set positions 4 and 5 of the function switch “SW1” to ON (closed) for a HI trip setpoint or OFF (open) for a LO trip setpoint (Figure 4).
3. Set position 6 of function switch “SW1” to ON for non-failsafe operation or OFF for failsafe operation (e.g. alarm trips upon power failure).
4. Set positions 7 and 8 of function switch "SW1" to upscale or downscale burnout.

1. After configuring the DIP switches, connect the input to a calibrated t/c source and apply power. Refer to the terminal wiring in the Specifications section
2. Starting Calibration: After applying power to the unit all three LEDs will flash for approximately 10 seconds. Next, input the signal level for Relay “A” setpoint, the green LED should be on. Press the CAL button and hold for 4 seconds (until the red LED starts flashing) to enter the calibration mode. The green LED should be on and the red Relay “A” LED should now be flashing.
3. Setpoint “A”: Input the desired trip level for Relay “A”, if not already done, and push the CAL button. The green and the red Relay “A” LED should be flashing. Note, the green LED will stop flashing when the input drops below a high setpoint or rises above a low setpoint.
4. Deadband “A”: For minimum deadband (0.25% approx.), press and hold the CAL button for 4 seconds. For high setpoints lower the input level (green LED turns off) to the desired deadband point and push the CAL button. For low setpoints increase the input level to the desired deadband level and push the CAL button. The green LED should be on and the red Relay “B” LED should be flashing.
5. Setpoint “B”: Input the desired trip level for Relay “B”, and push the CAL button. The green and the red Relay “B” LED should be flashing.
6. Deadband “B”: For minimum deadband (0.25% approx.), press and hold the CAL button for 4 seconds. For high setpoints lower the input level (green LED turns off) to the desired deadband point and push the CAL button. For low setpoints increase the input level to the desired deadband level and push the CAL button. The green LED should be on and both the red LEDs should be flashing.
7. Press the CAL button one final time to exit the calibration mode. Check the setpoint and deadband to validate calibration.

Relay Protection and 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 0.1mF pulse film capacitor (foil polypropylene recommended) of sufficient voltage, and a 47W, 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).