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2-4 Model 2790 SourceMeter

Switch System User’s Manual

I-source – channels 21, 22, 24, and 27

The programmable I-source (0 to 50mA) is used as the test current to measure low resis-

tance (inﬂator bridgewires and shunt bars).

• The I-source is designated as channel 27.

• Opening channel 22 selects the I-source.

• Closing channel 21 connects the I-source.

• Closing channel 24 connects the dry circuit clamp for the shunt bar test (20mV,

1mA limit).

NOTE “Ohms speciﬁcation calculations” in Appendix A explains how to determine the

accuracy speciﬁcation for source levels not speciﬁed in the “7751/7752/7753

Source/Switch Module Speciﬁcations” sheet.

V-source and I/V ampliﬁer (7751/7753 only) – channels 21, 22, 23, 28

The programmable voltage source (50 to 500V) and I/V ampliﬁer are used to measure

high resistance (insulation resistance of an inﬂator).

• The V-source is designated as channel 28.

• Closing channel 22 selects the V-source.

• Closing channel 21 connects the V-source.

• Closing channel 23 connects the I/V ampliﬁer.

WARNING Do not connect V-source Hi to earth ground. The 7751/7752/7753 mod-

ule uses a ﬂoating ground. This ﬂoating ground is not connected to

safety earth ground. Not only will it create a shock hazard by ﬂoating

up to 500V, it will also effectively connect a 1nF capacitor across the

V-source, providing energy storage that could ignite an airbag under

fault conditions.

NOTE “Ohms speciﬁcation calculations” in Appendix A explains how to determine the

accuracy speciﬁcation for source levels not speciﬁed in the “7751/7752/7753

Source/Switch Module Speciﬁcations” sheet.

Cable discharge (7751/7753 only) – channel 20

A cable discharge circuit is used to dissipate charge build-up on the inputs to prevent acci-

dental ignition of the inﬂator. For details, see “Cable discharge circuit”.

• Closing channel 20 discharges voltage on the input channels.

Keithley 2790 User Manual

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