Fluke 52120A, User Manual

Page: 77 / 98

Calibration
Introduction
5
5-7
How to Use 8508A Math Functions to Simplify Error Corrections
In the procedure below, the 8508A ‘*m’, ‘-c’, ‘÷z’ and ‘%’ Math functions are used to
give the measurement result as a percentage error that can be directly compared to the
product specification. Refer to the 8508A Users Manual for description of the math
functions and their operation. The math is:
(
(Correction x measured value [*m] – reference value [-c])
)
X 100
Reference value [÷z]
For each A40B shunt, calculate and type in the correction into the *m store. The
reference value comes through the 8508A rear input from the 5720A. Disable all Math
operations before the measurement sequence starts. With the characterized voltage
applied at the rear input of the 8508A, use the Last Reading and Enter keys to store the
current measurement into–c and ‘÷z’ stores. Set the 8508A input to the front terminals.
Turn on ‘*m’, ‘-c’, ‘÷z’ and ‘%’.
For example, a correction value of 0.999900 is stored in ‘m’. The reference value from
the 8508A rear input is stored in ‘c’. ‘z’ is set to 0.800008 V. The measured value from
the front input is 0.799881 V. The percentage of error is calculated as:
(
(0.999900 x 0.799881 – 0.800008)
)
X 100
=
–0.0259 %
0.800008
The system characterization procedure is not necessary for dc measurements. You make
dc measurements with the 5720A output connected to the Product input and then measure
through the A40B with the 8508A. The ‘-c’ and ‘÷z stores are preloaded with the
expected voltage output from the shunt. For all of the shunts, the output is 0.8 when the
input is full range. The correct values are shown in the verification results table. The ‘*m’
store has the correction factor for the shunt used for the measurement. The accuracies of
the 5720A, A40B shunt, and 8508A are summed with the noise and shunt power
coefficient by root-sum-of-squares (RSS) to get the measurement uncertainty.
Equipment Setup
Setup the equipment as shown in Figure 5-1. Use the 2A A40B shunt for the shunt in the
figure. Push
V
on the Product. Set the DMM (8508A) to the 2 volt range. Set the DMM
to Input front. When the 5720A outputs dc, the DMM must be set for dc volts. When the
5720A outputs ac, the DMM must be set for ac volts. Configure the DMM for a rolling
average of four measurements (MATH CONFIG, R, select 4, MATH AvR).
To maximize Product and shunt warm-up time, set the Product in operate (OPR) mode
for the 8508A rear input measurements.
2 Amp Range Verification
1. Set the 5720A output to +1 Vdc and push
M
on the 5720A.
2. Push
B
on the Product.
3. Push
M
on the Product.
4. Set the DMM ‘m’ store to the 2 A shunt correction factor.
5. Set the DMM ‘-c’ and ‘÷z’ stores to 0.4.
6. Turn on the ‘*m’, ‘-c’ and ‘÷z’, and % math functions on the DMM.
7. Let the measurement become stable for a minimum of one minute and then record the
measured error in Table 5-3.
8. Set the 5720A output -1 V dc.
9. Set the DMM ‘-c’ and ‘‘÷z’ stores to 0.4. Record the measure error.