Lake Shore 625, Руководство пользователя

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Lake Shore Model 625 Superconducting MPS User’s Manual
Service 7-5
7.7 OUTPUT SOURCE IMPEDANCE
The current output of the Model 625 has a 25 Ω source impedance, resulting from a 25 Ω resistor across the output
terminals. This is necessary to keep the output of the power supply stable into the purely inductive load of a
superconducting magnet. This is common practice in many superconducting magnet power supplies. This typically
results in negligible error when driving a superconducting load. The displayed output current is compensated for the
current loss through the resistor and reflects the actual current in the magnet.
This impedance can cause unexpected results in systems that have larger than normal lead resistance or other resistive
impedance. If there is a voltage across the output terminals of the supply, then a small amount of current will flow
through the stabilizing resistor given by the equation I = V/25, where I is the current through the resistor and V is the
voltage across the output terminals. This will reduce the amount of current flowing through the magnet. The output
current reading is compensated for the current flowing through the resistor and is representative of the current in the
magnet. If it is necessary to have the current in the magnet exactly equal a certain value, the output current setting can be
increased until the output current reading is equal to the desired amount.
In some circumstances it may be desirable to disable the reading compensation. In this case, the output current reading
will closely match the output current setting, but the reading may not be indicative of the current in the magnet since the
current in the resistor is not accounted for. To disable the reading compensation of the source impedance, send
CALCOMP 1 over the computer interface. To turn on the reading compensation, the default setting, send CALCOMP 0
over the interface. To make the change nonvolatile, send the CALSAVE command after setting the compensation or else
the previous setting will be used at the next power up.
There are some magnet systems in which the 25 Ω output resistor is not necessary for stable operation. Many of the
magnets that have a persistent switch have enough resistance for the power supply to operate properly. In this case, the
resistor can be removed and the reading compensation shut off in software. Please contact Lake Shore for further
information on removing this resistor.
CAUTION: If the 25 Ω output resistor is removed and the power supply is operated on a magnet without enough
resistance, the power supply can go into oscillation possibly quenching and damaging the magnet.
Please contact Lake Shore before attempting this procedure.
7.8 ELECTROSTATIC DISCHARGE
Electrostatic Discharge (ESD) may damage electronic parts, assemblies, and equipment. ESD is a transfer of electrostatic
charge between bodies at different electrostatic potentials caused by direct contact or induced by an electrostatic field.
The low-energy source that most commonly destroys Electrostatic Discharge Sensitive (ESDS) devices is the human
body, which generates and retains static electricity. Simply walking across a carpet in low humidity may generate up to
35,000 volts of static electricity.
Current technology trends toward greater complexity, increased packaging density, and thinner dielectrics between
active elements, which results in electronic devices with even more ESD sensitivity. Some electronic parts are more
ESDS than others. ESD levels of only a few hundred volts may damage electronic components such as semiconductors,
thick and thin film resistors, and piezoelectric crystals during testing, handling, repair, or assembly. Discharge voltages
below 4000 volts cannot be seen, felt, or heard.
7.8.1 Identification of Electrostatic Discharge Sensitive Components
The following are various industry symbols used to label components as ESDS.