valutazioni - 3, GPA: 3.7
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The sensing leads should be connected as close to the load as possible. If slightly degraded CV load regulation can be tolerated, the power supply will provide remote voltage sensing with up to 2 Vdc drop in each load lead and with more than 0.2 ohms resistance in each sense lead. As the voltage drop in the load leads increases, the load voltage error due to sense-lead resistance increases according to the formula: (2Rs + 0.5)V1 1000 where Rs is the resistance in ohms of each sense lead and Vl is the voltage drop in each load lead. For example, if the resistance in each sense lead is 1 ohm and the voltage drop in each load lead is 2 Vdc, the load voltage might differ by [2(1) + 0.5] 2/1000 = 5 mVdc from that with no sense-lead. The sensing leads are part of the supply’s programming circuits, so they should be connected in such a way as to make it unlikely that they might inadvertently become open circuited. If the sense leads open during operation, the voltage at the load will rise slightly above its’ programmed value. Note: The power supply includes protection resistors that reduce the effect of open sense leads during remote- sensing operation. If a sense lead opens there will be a change in the output voltage. See Table 3-4 for the approximate voltage change. Table 3-4. Voltage change due to open sense lead Model +S -S Both 6010A 1.6% -0.1% 1.5% 6011A 4% 1% 4.8% 6012B 1.6% -0.1% 1.5% 6015A 1.6% -0.1% 1.5% 6023A 4% 1% 4.8% 6028A 4% 1% 4.8% Operating Instructions 35 Analog Programming These instruments can obtain their output voltage and current programming information from three distinct sources: 1) locally from the front panel, 2) remotely from an external isolated, voltage source or, 3) remotely from an external isolated, resistance. Mode switches B1, B2, .through B6, located on the rear of these products, enable the user to make these selections. The remote analog programming signals are connected to rear-panel screw-on terminals. When the power supply is configured for remote voltage or resistance programming, the front panel VOLTAGE or CURRENT controls of the parameter being controlled are disconnected and have no effect on the output. Note: Switches B1, B2 and B3 are for selecting the programming source for the output current. Switches B4, B5 and B6 select the programming source for the output voltage. The source of the Constant Current programming information is selected independently from the source of the Constant Voltage programming information. Both can be done at the same time. Caution: The common terminal ( P) is internally connected to the minus (-) output terminal. If either output is grounded, the external programmer MUST be floating. Failure to float the programmer may result in significant damage to the power supply. For resistance programming, internal CV and CC current sources supply 1.25 mA currents through the programming resistors to create programming voltages for the power supply. A resistance of 0 to 4 K ohms will program the output voltage or current from 0 to full scale. A variable resistor can control the output over its entire range. Or, a variable resistor connected in series and/or parallel with a fixed resistor can have its control restricted to a limited portion of the output range. Alternatively, a switch can be used to select fixed values of programming resistance to obtain a set of discrete voltages or currents. Note: The switching configuration used may require make before-break contacts to avoid producing the output voltage transients caused by momentarily opening the programming terminals. To maintain the temperature and stability specifications of the power supply, any resistors used for programming must be stable, low-noise resistors with a temperature coefficient of less than 25ppm per °C and a power rating of at least 1/2 watt. Both voltage and current outputs can also be controlled by a voltage source. A voltage of 0 to 5 volts programs the output voltage or current from zero to full scale. Voltage sources of more than 5 volts can be scaled down to the proper range. The following paragraphs discuss in greater detail the methods of remotely programming the output voltage or current using either a resistance or voltage input. Whichever method is used, the wires connecting the programming device must be shielded to reduce noise pickup. The outer shield of the cable should not be used as a conductor, and should be connected to ground at one end only. Although the following setup drawings (Figure 3-7 through 3-11) show the supply strapped for local sensing, analog programming and remote voltage sensing do not interact and may be used simultaneously. Constant Voltage Output, Resistance Control. The setup shown in Figure 3-7 allows the output voltage to be varied by using an external resistor to program the power supply. A programming resistor variable from 0 to 4000 ohms produces a proportional output voltage from zero to full scale. Note that fixed resistors may be ...
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