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2.5.2
Shielding, Grounding, and Noise
For noise reduction, tightly twist and shield the leads from the MPS to the magnet. Connect the shield to the
MPS chassis as shown in figure 2-4.
WARNING:
DO NOT place magnet leads in contact with other MPS/system connections or metal parts.
In some instances, the user's measurement leads may pick up noise from the magnet leads. Although this
common mode noise may affect the user's measurement it rarely affects the current in the magnet. If the
user's measurement is earth grounded, some improvement is almost always possible by tying the –OUT
terminal of the MPS to earth ground – either at the MPS chassis or, if the user's system has one, the common
system earth ground point.
WARNING: If the – OUT terminal is tied to earth ground, make certain the +OUT cable from the MPS
contacts no other earth ground point - it forces the MPS output current into this other ground point. If
the other ground point is a small wire, it may melt or catch fire.
2.5.3
MPS Remote Inhibit and Fault Indicator Connections
The MPS has a Fault Indicator
(FLT) output and a discrete
Remote Inhibit (RI) input which
are both interface independent
and provide fault indication and
remote output shutdown in the
event of catastrophic failure. The
Fault Indicator relay contact is
open when the MPS detects no
faults. When the MPS detects an
internal fault, a remote inhibit, or
an output inhibit, it lights the front
panel Fault LED and closes the
relay contact. The contact closure
alerts other system components
of the fault. In an auto-parallel
system (up to four MPS units
connected in parallel) these
signals connect in parallel
between each of the MPS units
(See Paragraph 2.6 for details on
connections between two auto-
parallel units). Make connections
to a rear panel detachable
terminal block defined in Table 2-
3 and Figure 2-2.
2.5.4
AC On Indicator
The MPS provides a discrete ON indicator. Terminals 5 and 6 on the terminal block connector, shown in
Figure 2-2 above, connect to relay contacts that close when the front panel circuit breaker is in the ON
position. There is also a front panel LED that lights when the MPS is ON and connected to AC power.
2.5.5
OVP Connection
In auto-parallel MPS configurations, this connection synchronizes the firing of the Over Voltage Protection
(OVP) circuits of each MPS (see Chapter 5). See Paragraph 2.6 and Figure 2-5 for auto-parallel connections.
2-4
Lake Shore Model 647 Magnet Power Supply User's Manual
TERMINAL
1
2
3
4
5
6
7
8
LABEL
Remote Inhibit – Active low, TTL-compatible input to
RI+
remotely force the output settings to 0 A and 1 V. Also
RI–
activate RI by shorting +RI to -RI with a relay contact closure
or a switch.
FLT+
Fault Indicator – A relay contact that closes to indicate a
FLT–
fault. Contact rating: 0.25 A resistive at 100 VDC, 3 W, 25
VA.
ON Indicator – A relay contact that closes to indicate when
ON+
the front panel circuit breaker is in the ON position. Contact
ON–
rating: 0.25 A resistive at 100 VDC, 3 W, 25 VA.
NONE
Factory Use Only. Do not connect to this terminal.
In auto-parallel MPS configurations, OVP ensures that the
OVP
activation of one MPS Over Voltage Protection circuit
activates all the other parallel MPS units' protection circuits.
Table 2-3 RI, FLT, ON, and OVP Connections
Figure 2-2 RI, FLT, ON and OVP Connections
DEFINITION
Setup & Connections
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