The Q108 is equipped with three front panel LEDs. The green LED is a dual function LED labeled IN. This LED indicates line power and input signal status. Active DC power is indicated by the illuminated LED. If this LED is off, check DC power and wiring connections. If the input signal is 10% above or below the configured input range Protecting the Integrity of Industrial Process Signals An Invensys Company the green LED will flash at 8Hz or 4Hz, respectively. Two red LEDs indicate the relay state for each setpoint. An illuminated red LED indicates the tripped condition.
The Q108 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.
The field configurable Q108 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.
LSI circuitry in the Q108 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.
Unless otherwise specified, the factory presets the Model Q108 as follows:
||A, B: 0.25%
The DC power input accepts any DC source between 9 and 30VDC.
Note: An I/QRail is an optional accessory to power the modules. A two, four, or eight position rail is available. See ordering information.
For other I/O ranges, refer to Table1 and Figure 4. Reconfigure switch SW1 for the desired input type, range and function.
WARNING: Do not attempt to change any switch settings with power applied. Severe damage will result!
With the module removed from the rail and not powered, snap off the face plate by lifting the right edge away from the heat sink. Note the input switch (SW1) is located under the face plate. Set positions 9 & 10 for voltage or current input (see Table1).
Set positions 1 through 4 of input range switch “SW1” for the desired input range (see Table 1).
Set position 5 of input range switch “SW1” to ON (closed) for unipolar (e.g. zero based, 0-20mA) range or OFF (open) for bipolar (e.g. -100% offset, -20 to 20mA) range (see Figure 4).
Set positions 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).
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).
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).