pin 2 falls below 24 volts for a continuous 1- second interval. The hardware and software responds to this condition by turning off the power source to pin 2 and flashing the pin 2 LED as a warning. After a 5-second “cool-down” interval the output returns to the same condition as upon initial power up. Power is again applied to pin 2, the pin 2 status LED will light, and monitoring won’t begin for another five sec- onds. A full short-circuit condition applied to the Model 45’s 2-wire connectors will result in a continuous cycle of six seconds on (five seconds for start up and one sec- ond for detection) and five seconds off.
As a diagnostic aid the 2-wire (PL) power status LED associated with pin 3 always remains active, even when the Model 45 is supplying power to the 2-wire party-line intercom circuit. Whenever DC in excess of approximately 18 volts is present on pin 3 the LED will light. This condition will typically not exist but could prove useful in special circumstances.
2-Wire Circuit Serves as the Unit’s Power Source
If no external source of 24 volts DC is connected and configuration DIP switch 1 is in its on (up) position, the connected
2-wire party-line circuit can provide power for the Model 45. If this condition is active the 2-wire (PL) input power LED will light. The 2-wire (PL) power status LED will also be lit, indicating that power in excess of 18 volts is detected on pin 2. The pin 3 LED will also light if the same condition is present on pin 3.
Level Meters
The Model 45 contains four 5-segment LED level meters. These meters are provided
as a support aid during installation, con- figuration, operation, and troubleshooting. The meters represent the strength of the signals coming in from, and going out to, the 4-wire connections. The meters are or- ganized in two groups each representing one input and one output. They are cali- brated to reflect the level in dB relative to +4 dBu. This is similar to the way in which now-legacy VU meters functioned. As an example let’s take the situation where an output (“to 4-wire”) LED labeled 0 dB is lit. (For this example, the level on the 2-wire party-line circuit is just large enough to light the 0 LED.) This indicates that a sig- nal with an approximate level of +4 dBu is present on the associated 4-wire output connector.
Each level meter contains four green LEDs and one yellow LED. The four green LEDs indicate signal levels at or below +4 dBu. The top LED is yellow and indicates a sig- nal that is 6 dB or greater than the +4 dBu nominal level. An audio signal that causes the yellow LED to light doesn’t necessarily indicate an excessive level condition, but it does provide a warning that at some stage reducing the signal level may be prudent. Typical operation with normal signal levels should find the meters lighting near their 0 dB point. Signal peaks may cause the yellow LEDs to flash. But a yellow LED that lights fully during normal operation will typically indicate a signal level or configu- ration problem.
If the meters consistently display lower or higher levels than their 0 dB points it’s possible that a configuration issue exists. This would typically be related to incor- rect settings on the equipment connected to the 4-wire inputs and outputs. It’s pos- sible that although a connected 4-wire
