Specifications

Comments • The strain gage wiring diagram used for this example is on page 28.

The diagram showing how the HP 3458A Multimeter is connected to

the FET strain gage multiplexer is on page 32.

• When making strain measurements with an external voltmeter, the

following voltages are measured in the sequence shown:

bridge output voltage (Vout: channels 100 - 102) unstrained

bridge excitation voltage (Vs: channel 115) unstrained

bridge output voltage (Vout: channels 100 - 102) strained

bridge excitation voltage (Vs: channel 115) strained

These measurements are used to compute Vr, which in equation

form is defined as:

Vr = [(Vout/Vs)strained - (Vout/Vs)unstrained]

Vr is then substituted into the equation (Table 4-1 on page 52) for

⁄

bridge measurements.

• The channel closed/measurement handshake sequence between the

FET multiplexer switchbox and the voltmeter occurs over the

multiplexer’s digital bus. When connected as shown in Figure 2-8,

the digital bus cable (HP Part Number E1411-80001) connects the

multiplexer’s "channel advance" and "channel closed" pins to the

voltmeter’s "VM Compl" and "Ext Trig" ports, respectively. Thus,

when a multiplexer channel is closed, a "channel closed" pulse from

the multiplexer is applied to the voltmeter’s "Ext Trig" port. When

the voltmeter measurement is complete, the voltmeter complete

signal triggers the multiplexer via the "channel advance" line.

Continued on Next Page

44 Making Strain Gage Measurements Chapter 3

Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com