100/180 mm PAPERLESS GRAPHIC RECORDER: USER GUIDE
HA028910
Issue 13 Sep 16
User Guide
Page 384
WORST CASE ERROR CALCULATION
Assuming type T thermocouple at 350˚C, ambient temp = 40˚C, CJC = internal.
Total error = input error + range error + temperature error +linearisation error + cold junction error.
Input error:
From thermocouple tables, a type T thermocouple generates a voltage of 17.819mV at 350 ˚C. From the
dc performance table above, the maximum error is 0.030% input = 0.03 x 17.819/100 = 5.346µV
Range error:
The 38mV range is used as the type t thermocouple is defi ned to cover the range -270˚C (-6.258mV) to
+400˚C (20.872mV). From the dc performance table, the maximum range error is 0.052% range, and the
range is 38 + 38 = 76 mV. Thus the maximum range error is 0.052 x 76/100 = 39.52µV.
Temperature error:
The dc performance table above is specifed at 20˚C, but the ambient in this example is 40˚C. From the
dc performance table, the worst case temperature performance is 25ppm/˚C, so our error is 25 x (40-20)
x 17.819 x 10
-6
= 8.910µV.
Linearisation error:
From the thermocouple table, the maximum linearisation error for a type t thermocouple is 0.02 ˚C
Cold junction compensation (CJC) error:
The internal CJC error is 1˚C maximum with the instrument at 25˚C. The CJC rejection ratio is 50:1, so a
further error of (40-25)/50 = 0.30 ˚C may occur, giving a total maximum CJC error of 1.3˚C.
Maximum error
From the above, the total error adds up as follows:
Input error:
5.346µV
Range error:
39.520µV
Temperature error: 8.910µV
Linearisation error:
0.02˚C
CJC error:
1.30 ˚C
Total error:
53.776µV + 1.32˚C
From thermocouple tables, a change of 1˚C is equivalent to a change of 60µV, so a change of 53.776µV is
equivalent to a change of 0.896˚C.
Thus the total worst case error for this example is (0.896 + 1.32) = 2.216˚C
