Section 8. Operation
Error Calculations with Input Reversal = False
µV error = gain term + offset term
= (44500 µV * 0.12%) + (3 * 66.7 µV + 2.0 µV)
= 53.4 µV + 200 µV
= 7.25 µV (= 7.25 °C)
Ground Looping Error
When the thermocouple measurement junction is in electrical contact with the
object being measured (or has the possibility of making contact), a differential
measurement should be made to avoid ground looping.
Noise Error
The typical input noise on the ±2_5 mV range for a differential measurement with
16.67 ms integration and input reversal is 0.19 μV RMS. On a type
-T
thermocouple (approximately 40 μV/
°
C), this is 0.005
°
C.
Note
This is an RMS value; some individual readings will vary by greater than
this.
Thermocouple Polynomial Error
NIST Monograph 175 gives high-order polynomials for computing the output
voltage of a given thermocouple type over a broad range of temperatures. To
speed processing and accommodate the CR1000 math and storage capabilities,
four separate 6th-order polynomials are used to convert from volts to temperature
over the range covered by each thermocouple type. The table
Limits of Error on
CR1000 Thermocouple Polynomials
(p. 334)
gives error limits for the thermocouple
polynomials.
Table 68.
Limits of Error on CR1000 Thermocouple Polynomials
TC
Type
Range °C
Limits of Error °C
Relative to NIST
Standards
T
–
270
to
400
–270
to
–200
18 @ –270
–200
to
–100
±0.08
–100
to
100
±0.001
100
to
400
±0.015
J
–
150
to
760
±0.008
–100
to
300
±0.002
E
–
240
to
1000
–240
to
–130
±0.4
–130
to
200
±0.005
334
Summary of Contents for CR1000
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Page 456: ...Section 8 Operation Figure 118 Real Time Custom 456 ...
Page 457: ...Section 8 Operation 8 8 1 3 Final Memory Tables Figure 119 Final Memory Tables 457 ...
Page 458: ...Section 8 Operation 8 8 2 Run Stop Program Figure 120 Run Stop Program 458 ...
Page 460: ...Section 8 Operation Figure 122 File Edit 460 ...
Page 461: ...Section 8 Operation 8 8 4 PCCard Memory Card Display Figure 123 PCCard CF Card Display 461 ...
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