6.0 DRAWINGS
Figure 6-1 504 Case Dimensions
Figure 6-2. 504 Preamp Block Diagram
Figure 6-3. 504 Postamp Block Diagram
APPENDIX A - TRANSMITTER
ACCURACY SPECIFICATIONS
The complex current-transmitter circuitry necessary to amplify,
isolate, protect, and offset weak input signals while consuming
only small amounts of power can distort the signal in many ways.
Many transmitter data sheets omit key accuracy factors and/or
express performance in percentage values without mentioning the
full-scale value. Design limitations can be disguised by such
"specsmanship"; the 504 specifications, however, are detailed
in order to present the complete performance accuracy.
504 input errors are logically expressed in microvolts, and output
errors are readily expressed in microamperes, since output is
current. Transmitter users, however, are rarely interested in
microamperes. Therefore, these output current errors are translated
back to input microvolts as a percentage (or ppm) of the selected
Span.
Another fundamental division of errors is that of independence
or dependence on Zero and Reading. Resistor aging and tempco mismatch
in the Zero and Voltage Reference circuits will produce errors
which increase with Zero suppression but which are independent
of the amount of Reading (value above the Zero).† Resistor
aging and tempco mismatch in the amplifier gain (feedback) circuits
will usually affect both Zero and Reading accuracy; amplifier
gain tempco variations are important to just the Reading stability.
A complete error specification needs a term proportional to Zero
(suppression) and a term proportional to Reading.
In addition to the Zero and Span tempco (ambient temperature effects),
there are other possible errors, often referred to as "hysteresis,"
"repeatability," "drift," or "time" errors. No statistically significant
errors of these types have yet been observed for the 504,which
utilizes a solid-state, band-gap input voltage reference, matched-pair
input PNP transistors, integrated-circuit current source and imbalance
control, and matched-tempco bridge resistors. The 504 also provides
a variable-tempco output adjustment (factory-set) which eliminates
many of the errors lumped in this category for other units. Its
specification includes a 10 uV tolerance for the calibration accuracies.
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