Lake Shore 370, Руководство пользователя

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Lake Shore Model 370 AC Resistance Bridge User’s Manual
3.4.6 Temperature Sensors
Temperature sensors should be treated as any other resistor being measured. One difference is that four lead devices are
normally calibrated with a specific arrangement of current and voltage leads. Follow all manufacturer recommendations
on installation including lead arrangement or errors in temperature measurement will result.
3.5 OPTIONAL SCANNER INSTALLATION
The Model 3716/L and 3708 Scanners expands the input capability of the Model 370 and increase the number of input
channels to 16 (3716/L) or 8 (3708). It is an extension of the isolated measurement circuitry of the Model 370 so its
installation should follow the guidelines described in Paragraph 3.4 as well as this paragraph. Cables between the
scanner and Dewar should be as short as possible because they carry the smallest signals. Cables between the scanner
and instruments can be longer.
3716 FrontRear.bmp
Figure 3-7. Model 3716 Scanner Front and Rear Panels
3.5.1 Grounding the Scanner
It is important to note that the enclosure of the Model 3716/L and 3708 is connected to the input cable shield and
therefore tied to measurement common (not the chassis) of the Model 370. In most installations the shield screw on the
enclosure should be ground strapped to the test Dewar creating
the
single connection between measurement circuits and
Earth. If a different shield to Earth connection is preferred the scanner enclosure must be electrically insulated from its
surroundings.
3.5.2 Scanner Resistor Input Connector Definition
With the Model 3716/L, four 25-pin D subminiature receptacles hold connections for up to sixteen 4-lead resistor inputs
in four sets of four. With the 3708, two 25-pin DIN receptacles hold connections for up to eight 4-lead resistor inputs.
They mate with 25-pin D subminiature plugs included with the scanner (Lake Shore P/N 106-253). Unused inputs can
either be left open or all four measurement pins can be shorted together. Pin connections for Channels 1–4 are shown in
Figure 3-8, Channels 5–8, 9–12, and 13–16 are wired the same way.
3.5.3 Scanner Resistor Input Cabling
The cable between scanner and Dewar should be kept as short as possible without causing strain on the cable or
connections. See Figure 3-6. Short cables can improve the measurement in several ways. They minimize the potential for
induced noise on the smallest voltage signals, limit cable capacitance that cannot be guarded because the guards are not
carried through the scanner and reduce the potential for ground loops if shield lines accidentally touch the Dewar.
Individually shielded, twisted pair cable is recommended for wiring the resistor inputs. Cable containing up to 8 shielded
pairs of wire is available form electronics distributors so one cable can provide enough wires to connect the four
channels of one input connector. If multiple smaller cables are used they should be wrapped together to minimize ground
loops. The two current leads of a channel should be twisted and the two voltage leads should be twisted. The input
connectors provide several shield pins so that individual shields can be connected separately at the scanner end of the
cable.
If the shield screw on the scanner enclosure is strapped the test Dewar, the cable shield can be left unterminated at the
Dewar end. If the scanner enclosure is not connected to the Dewar, the shields of the cable should be terminated at the
Installation 3-7