\rIII. THERMOCOT]PLES
, A. Troubleshooting
ControlCircuit
a)anopenthermocouplewill inhibittheconirolfrom operating
b)a shortedthermocouplewill causethecontrolto run awaysinceit defaultsto roomtempemture
c)a reversedwiredthermocouplewill causetheconfiolto readbackwardsandrunaway
Shortingthe thermocoupleis a goodway to seeif the controlquickly respondsby comingon during
troubleshootingSince. shortingthethermocoupleis thesameasbridgingthecircuit,it will defaultto room temperatureandnaturallycall for heatif thepotentiometeris setat a highertemperatureWhen.perform- ing thisvery brief TEST,besureto removettrreshortfrom thecircuit beforeplacingthegriddlebackinto service.
ThefollowingchartliststheTypeKthermocouplemillivoltreadingfrom200"F(93"C)to 500"F(26trC).
GriddleTemperature
Junction 200eF 300eF 400eF 500eF
Temp (93rC) (149sC) 204ec) (260ec)
90eF(32rC) 2.s2 4.80 7.02 9.27
85eF(29e 2.U 4.91 7 . 1 3 o ? a
SorF(zFC) 2.75 5.02 725 9.49
7seF(24eC) 2.86 5 . 1 4 7.36 9.60
70eF(24eC) 2.98 5.25 7.47 9.72
65e(18eC) 3.09 5.36 t . c 69.83
60eF(16eC) 3.2A 5.47 7.69 9.94
Example:Thethermocouplemillivolt readingat 300'F(149"C)with ajunctiontemperatureof 85.F(29.C) shouldbe4.91mV.
At roomtemperaturegoodthermocouplewill
Coldresistancereading:6.5OHMSaverage.
t2
