KEPCO ATE-DMG SERIES - Manual (Page 35)

ATE-DMG 042314 3-1
SECTION 3 - OPERATION
3.1 GENERAL
Interconnections between an a-c power source and a stabilized power supply, and between the
power supply and its load are as critical as the interface between other types of electronic equip-
ment. If optimum performance is expected, certain rules for the interconnection of source, power
supply and load must be observed by the user. These rules are described in detail in the follow-
ing paragraphs.
3.1.1 SAFETY GROUNDING
National and international safety rules dictate the grounding of the metal cover and case of any
instrument connected to the a-c power source.
WARNING
KEEP INSTRUMENT GROUNDED WHILE IT IS CONNECTED TO THE
A-C POWER SOURCE.
Kepco power supplies with a flexible a-c power cord are equipped with a 3-prong safety plug,
which must be connected to a grounded a-c power outlet.
3.1.2 D-C (OUTPUT) GROUNDING
Connections between the power supply and the load (load and sensing connections), as well as
connections to the power supply amplifiers (programming connections) may, despite all precau-
tions such as shielding, twisting of wire-pairs, etc., “pickup” radiated noise of a wide frequency
spectrum. To minimize these undesired effects, one side of the power supply output/load circuit
should be grounded.
Successful d-c grounding depends on careful analysis of the individual situation and only gen-
eral guide lines can be provided here. One of the major points, however, is to avoid GROUND
LOOPS. Ground loops are created when two (or more) points are grounded along the output cir-
cuit. Due to the wire impedance between the separated grounded points, a noise voltage is
developed which subsequently is superimposed on the load. The only way to avoid ground
loops is to investigate the output circuit (including the connected load) carefully by means of an
ohmmeter for any resistance to ground. A single d-c ground point can be selected only if the
output circuit is completely isolated. A single point is selected along the power supply out-
put/load circuit and this point is returned to ground with a single wire. The exact location of this
“best” d-c ground-point is entirely dependent on the application at hand. For single, isolated
loads, the d-c ground-point may be located directly at one of the output terminals of the power
supply which may be connected to ground. If error sensing is employed, d-c ground can be
established at the remote load. In case of an internally grounded load, the d-c ground is auto-
matically established directly at the load.
ATE Power Supplies have one side of the output returned to the case over a resistor/capacitor
combination (refer to Section 2, PAR. 2.6.1). In those cases, therefore, where the load is inter-
nally grounded, or where the signal ground must be established elsewhere, the resistor/capaci-
tor combination must be removed from the power supply case in order to avoid ground loop
problems. If there is a choice in selecting either the positive or the negative output of the power
supply for the d-c ground point, both sides should be tried, and preference given to the ground
point producing the least noise. Output ripple specifications (as measured at the output) are,