then proceed at a slower rate towards zero. The actual time required for the output to fall from two volts to zero will vary from several seconds to several minutes, depending upon which down-programming method is used.
3-20OPERATION BEYOND RATED OUTPUT
3-21 The shaded area on the front panel meter face indicates the approximate amount of output voltage or current that may be available in excess of the normal rated output. Although the supply can be operated in this shaded region without being dam- aged, it cannot be guaranteed to meet all of its performance specifications.
3-22OPTIONAL OPERATING MODES
3-23REMOTE PROGRAMMING, CONSTANT VOLTAGE
3-24 The constant voltage output of the power supply can be programmed (controlled) from a remote location if required. Either a resistance or voltage source can be used as the programming device. The wires connecting the programming terminals of the supply to the remote programming device should be twisted or shielded to reduce noise pickup. The VOLTAGE controls on the front panel are automatically disabled in the following procedures.
3-25 Resistance Programming (Figure 3-3). In this mode, the output voltage will vary at a rate determined by the voltage programming coefficient of 200 ohms/volt. The programming coefficient is determined by the programming current. This current is factory adjusted to within 1% of 5mA. If greater programming accuracy is required, it may be achieved by either adjusting R3 as discussed in Paragraph 5-88,or, if the instrument is equipped with Option 020, by adjusting potentiometer R112 as discussed in Paragraph 5-89.
Figure 3-3.Remet e Resistance Programming (Constant Voltage)
TM 11-6625-2958-14&P
3-26 The output voltage of the supply should be -15mV ±5mV when zero ohms is connected across the programming terminals. If a zero ohm voltage closer to zero than this is required, it may be achieved by inserting and adjusting R110 as discussed in Paragraph 5-83,or, if the instrument is equipped with Option 020, by adjusting potentiometer R113 as discussed in Paragraph 5-85.
3-27 To maintain the stability and temperature coefficient of the power supply, use programming resistors that have stable, low noise, and low temperature coefficient (less than 30ppm per degree Centigrade) characteristics. A switch can be used in conjunction with various resistance values in order to obtain discrete output voltages. The switch should have make-before-break contacts to avoid momentarily opening the programming terminals during the switching interval.
Figure 3-4.Remet e Voltage Programming,
Unity Gain (Constant Voltage)
3-28 Voltage Programming, Unity Gain (Figure 3-4). Employ the strapping pattern shown in Figure 3-4for voltage programming with unity gain. In this mode, the output voltage will vary in a 1 to 1 ratio with the programming voltage (reference voltage) and the load on the programming voltage source will not exceed 20 microampere. Impedance matching resistor (Rx) is required to maintain the temperature coefficient and stability specifications of the supply .
3-29 Voltage Programming, Non-Unity Gain (Figure 3-5). The strapping pattern shown in Figure 3-5can be utilized for programming the power supply using an external voltage source with a variable voltage gain. The output voltage in this configuration is found by multiplying the external voltage source by (Rp/RR).
3-30 External resistors Rp and RR should have sta- ble, low noise, and low temperature coefficient
