Precision instruments are almost always costlier than normal instruments. Unless you are working in a highly sofisticated research laboratory, normal instruments will appear quite satisfactory for most of the practical work. For example, consider two current sources A & B that can supply a maximum of 10mA current over a voltage range of 0 to 10V. Current source A is more accurate (+/- 0.1%) than current source B (+/- 1%). Connect 1K resistor across current source A & read IR drop by using 8 bit ADC (Analog to Digital converter). Similarly, connect another 1K resistor across current source B & read IR drop by using another 8 bit ADC. Both the ADCs are of same accuracy. Following observations can be obtained by this set-up >>>>>
Current Source A (accuracy = +/- 0.1%) : set current --- Actual Current --- IR Drop --- ADC value (mA) ------------- (mA) ----------- (mV) ------ (HEX)
0.2 ------------- 0.2002 ---------- 200.2 ---------- 05 1.8 ------------- 1.7098 --------- 1798.2 --------- 2E 2.6 ------------- 2.6013 --------- 2601.3 --------- 43 3.8 ------------- 3.7962 --------- 3796.2 --------- 61 5.2 ------------- 5.2052 --------- 5205.2 --------- 85 6.7 ------------- 6.6933 --------- 6693.3 --------- AB 7.8 ------------- 7.7922 --------- 7792.2 --------- C7 9.2 ------------- 9.2092 --------- 9209.2 --------- EC 10.0 ------------- 9.9990 --------- 9999.0 ------ (1)00Current Source B (accuracy = +/- 1%) : set current --- Actual Current --- IR Drop --- ADC value (mA) ------------- (mA) ----------- (mV) ------ (HEX)
0.2 ------------- 0.2020 ---------- 202 ------------ 05 1.8 ------------- 1.7820 --------- 1782 ----------- 2E 2.6 ------------- 2.6260 --------- 2626 ----------- 43 3.8 ------------- 3.7620 --------- 3762 ----------- 61 5.2 ------------- 5.2520 --------- 5252 ----------- 85 6.7 ------------- 6.7670 --------- 6767 ----------- AB 7.8 ------------- 7.7220 --------- 7722 ----------- C7 9.2 ------------- 9.2920 --------- 9292 ----------- EC 10.0 ------------- 9.9000 --------- 9900 -------- (1)0016 Channel Analyzer Report for Current Source A One point each in channel number 1,3,5,7,9,11,13,15 & 16
16 Channel Analyzer Report for Current Source B One point each in channel number 1,3,5,7,9,11,13,15 & 16Final report is the SAME for both accurate & inaccurate devices !!!