Model 7002Switch System Instruction Manual - Advanced Test ...

Front Panel Operation• INPUTON or OFF. Use this option to check or change the statusof the digital input line. Sense is fixed at active-high(ON=5V).4.15.1 Controlling digital circuitryEach of the four digital, open-collector outputs (connectorJ1006, pins 6, 7, 8, and 9) includes a built-in pull up resistorto +5V. The ouput transistor is capable of sinking up to100mA from voltages up to +30V.Early versions of the Model 7002 have an additional 10kΩresistor connected between the collector and the internalbuilt-in test circuitry. Under certain combinations of outputstates, this resistor limits the output high to 2.5V. Forexample:Output #1 set high (+5V)Output #2, #3, and #4 set low (0V)Actual output of digital output #1 is restricted to +2.5VIf using the digital output to sink current from external devices,a Model 7002 containing the additional 10kΩ resistorwill function correctly. The transistor switch is open, restrictingcurrent flow through the external device in the high state(+5V). However, if the output is directly used as an input toa typical logic input, the 2.5V high state may not be reliablydetected as a high. To correct this condition (if a 2.5V high isunacceptable), use one of the following solutions:• Add external 1kΩ pull-up resistors to the logic circuitinputs, or between the outputs and the +5V (pin 2) ofthe Model 7002.• Remove the built-in test resistors (R127, R131, R134,and R135).• Use an external voltage supply.External voltage supplyEach output can be operated from external voltage supplies(voltage range from +5V to +30V applied through the devicebeing driven). Refer to Figure 4-14 for a simplified schemat-ic of the digital I/O port. The high current sink capacity of theoutput driver allows direct control of relays, solenoids andlamps (no additional circuitry needed). Each output channelcontains a fly-back diode for protection when switching inductiveloads (such as a low power solenoid or relay coils).To use these fly-back diodes, connect the external supplyvoltage to pin 4 of J1006 (the digital I/O port). Make sure theexternal supply voltage is between +5V and +30V and currentrequired by the device does not exceed 100mA.CAUTIONDo not apply more than 100mA maximumcurrent or exceed +30V maximumvoltage on pin 4 of J1006 (the digital I/Oport). Applying current or voltage exceedingthese limits may damage the instrument.An externally powered relay connected to the digital outputport is shown in Figure 4-15. Other externally powered devicescan be similarly connected by replacing the relay withthe device. When using the Model 7002’s collector outputsto turn on externally powered devices, set the correspondingdigital output line parameters as follows (set parametersthrough the MAIN MENU>DIGITAL-I/O>OUTPUT-STATUS and OUTPUT-POLARITY menus):OUTPUT-STATUS=ONTTLX LOGIC-SENSE=ACTIVE-LOWNOTEThe X in TTLX represents the digital outputline number (TTL1 through TTL4).This parameter is set through the OUT-PUT-POLARITY menu by selecting thedesired digital output line number andpressing Enter.In the low state (0V), the output transistor sinks currentthrough the external device. In the high state, the output transistoris off (transistor switch is open). This interrupts currentflow through the external device. Most applications use active-low(ON=0V) LOGIC-SENSE. Use the LOGIC-SENSE menu to check or change the sense of each digitaloutput line.4-54