Agilent Technologies 90B manual Protecting Against Open Sensing Leads, Remote Sensing Connections

Figure 49. Remote Sensing Connections

Typically, the sensing current is 10mA or less. To insure that the temperature coefficient of the sensing leads will not significantly affect the power supply temperature coefficient and stability specifications, it is necessary to keep the IR drop in the sensing conductors less than 20 times the power supply temperature coefficient (stated in millivolts/°C). This requirement is easily met using readily available small size shielded two-wire cable--except in applications involving very long sensing leads of unusually well regulated power supplies with very low TC and stability specifications.

One end of the shield should be connected to the CP and the other end should be left unconnected. In nearly all cases this method of connecting the sensing shield will minimize ripple at the Load Distribution Terminals. However, in rare cases a different ground return point for this shield is preferable-- it is important in such cases to experimentally verify that this relative advantage applies under all possible combinations of load and line.

Protecting Against Open Sensing Leads

The possibility of an open remote sensing path, which might occur on a long-term or transient basis, should be avoided. Such open circuit conditions are likely if the remote sensing path includes any relay, switch, or connector contacts; any interruption of the connections between the power supply sensing terminals and the DC Distribution Terminals should be avoided wherever possible.

When a sensing open occurs, the regulator circuit within the supply reacts as though the load voltage were zero-

-usually, the output voltage corrects this deficiency by climbing rapidly toward the maximum rectifier voltage, a value which is significantly larger than the power supply's maximum rated output voltage. Even if the power supply output circuitry is designed to withstand this extreme, the chances are that the load is not.

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