Lake Shore 420, Руководство пользователя

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Lake Shore Model 420 Gaussmeter User’s Manual
Appendix A
A-5
Model 120CS
Current Source
Digital Voltmeter
+I
C
–I
C
+V
H
–V
H
+
–
I
C
V
H
R
L
Hall Generator
Load resistor required
for optimum linearity
(if specified)
C-450-U-C-3
Figure B-3 Typical Hall Generator Hookup
B4.0 USING A HALL GENERATOR WITH THE MODEL 420
To hookup a Hall generator to the Model 420 Gaussmeter, use a Lake Shore Model MCBL-6 Cable
Assembly. The cable is 200 cm (79 inches) long with a DA-15 connector on one end and four leads on the
other. The Hall generator is a four lead device. The four leads are lIc (Red), –Ic (Black), +VH (Blue),
and –VH (Yellow), corresponding to the four leads on all Hall generators except for cryogenic models (see
Paragraph B2.5).
The Model 420 has an input impedance of 420
Ω
. Therefore, the actual sensitivity at the gaussmeter input is
less than the value given with the Hall generator due to drop in the leads and cable. This is important because
a sensitivity value is supposed to load into the cable PROM to set calibration. We recommend the customer
always check accuracy against a reference field rather than use the sensitivity value sent with the bare Hall
generator. Because Lake Shore has no control of conditions beyond the cable, the customer must accept
responsibility for accuracy and compatibility.
Finally, Maganin wire is not usually acceptable for cryogenic installations because its resistance is often too
high. In cryogenic applications, Hall generators normally connect with twisted pairs of copper wire such as 34
gauge, Teflon insulated. There are two reasons for this:
1. The gaussmeter current source is normally limited in compliance voltage. The Model 420 should not drive
a load (Hall generator, Wires in cryostat, and probe cable) greater than 50
Ω
. For best performance, use a
load less than 30
Ω
.
2. Because the Model 420 input impedance is 420
Ω
, there is a voltage drop due to lead resistance in series
with the gaussmeter input. The Lake Shore Hall generator sensitivity given on the data sheet includes no
lead resistance. See Figure B-4.
Model 450
Gaussmeter Input
420 ž
Sensitivity at Gaussmeter input is
reduced by the lead/input voltage divider
R
cable
R
cable
R
cust
R
cust
Hall Generator
Open Circuit
Sensitivity
The gaussmeter needs input sensitivity
between 0.5 to 1.5 mV/kG at its input.
V
H
R
cable
= Lake Shore Model
MCBL-6 Cable Assembly
R
cust
= Customer
Supplied Leads
C-450-U-C-4
Figure B-4 Hall Generator Input Impedance