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 relay strain gage multiplexer (via the mainframe) is on
page 31
.
•
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) for
1
⁄
4
bridge
measurements.
•
The HP E1300/E1301 mainframe’s "Event In" and "Trig Out" ports are
connected to the voltmeter’s "VM Compl" and "Ext Trig" ports,
respectively. Thus, when a multiplexer channel is closed, a "channel
closed" pulse from the mainframe’s "Trig Out" port is applied to the
voltmeter’s "Ext Trig" port. When the voltmeter measurement is
complete, the voltmeter complete signal is applied to the "Event In" port
which triggers the multiplexer to close the next channel in the list.
42 Making Strain Gage Measurements
Chapter 3
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