Arbiter Systems 1088A, Руководство по эксплуатации

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58 Timing, IRIG-B and Pulses
7.2 Timing Output Description
When viewing the rear panel of the Model 1088B, you will see that there are a number of different
types of connectors as illustrated in Figure 7.1. Generally, there is a power inlet connector, a GPS
antenna connector, one DB-9 serial connectors, a series of four connector plugs and one option
plate. The hole plugs cover the connector holes for option Slot A, and the option plate covers Slot
B, used to house accessory boards that provide additional functionality to the 1088B.
Figure 7.1: Rear Panel Descriptions
7.2.1 Standard Inputs/Outputs
The Model 1088B has four BNC female connectors that can supply up to twenty-two different
timing signals to external equipment. Two of these connectors (J3 and J4) may also be configured
for an event/deviation inputs. All of the outputs are designed for digital and analog signals that
are configured using internal jumpers. Signals supplied to the digital drivers include unmodulated
IRIG-B, many different pulse outputs per second, and programmable pulse.
7.2.2 Digital Drivers
Each digital output is driven by one of the four outputs from a single CMOS 74HC126 quad driver
capable of supplying 18 mA (each) at 5 Vdc. To determine the maximum number of devices that
each digital driver can support, you will need to determine the load current, or input impedance,
for each connected device. For example, if the IED timing input signal (e.g. IRIG-B003) requires
1 mA, one output channel should be able to support 18 such devices. If the load current is more
or less, then you can connect any number of devices up to the current limit for one output.
7.2.3 Analog Drivers
The 1088B has one analog driver per output available for modulated IRIG-B signals and
±
5 V
deviation for a chart recorder. Additional analog drivers may be added as options (e.g. Option
03, 27, 29). The analog driver uses a series of LF353 op amps, which supply a 10 Vpp signal
through a 557-ohm source resistor, or 4.5 Vpp on Option 27, to IED’s. With increasing load
current from external IED’s more voltage is dropped across the clock source resistor and the drive
voltage decreases. Matching the modulated IRIG-B output voltage to the IED input is sometimes
critical, so it is important to match the modulated IRIG-B peak-to-peak voltage to within the
specified range of the IED. Table 7.1 shows how the actual drive voltage varies with increasing load
current. For IED’s with a restricted input range, it may be necessary to match the available drive
voltage to the IED through a small dropping resistor.