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Dear all,

This is my first time using an AM25T multiplexer with a CR6 datalogger for Type-K thermocouple measurements, and I am encountering an intermittent issue.

At times, the reference temperature (RTempC) becomes NAN, and simultaneously all thermocouple readings also become NAN without any apparent reason. After a few hours, the reference temperature recovers automatically, and all thermocouple readings return to normal.

Within a 24-hour period, this has occurred several times. Occasionally, the readings remain NAN for 3 to 4 hours before recovering.

Below is my CR6 program:

Const Num_T = 10
Dim i

Public BattV
Public PTempC
Public RTempC
Public T(Num_T)

Units BattV = Volts
Units PTempC = °C
Units RTempC = °C
Units T = °C

StationName TC2601

DataTable(TC2601,True,-1)
  DataInterval(0,10,Min,10)
  Average(1,BattV,FP2,False)
  Average(Num_T,T,FP2,False)
EndTable

BeginProg
  Scan(60,Sec,1,0)
    Battery(BattV)
    PanelTemp(PTempC,60)
    
    BattV = Round(BattV,2)
    PTempC = Round(PTempC,2)
    
    AM25T(T(),Num_T,mV200C,1,U5,TypeK,RTempC,U1,U2,U3,True,1000,60,1,0)

    RTempC = Round(RTempC,2)
    For i = 1 To Num_T
     T(i) = Round(T(i),2)
    Next i
    
    CallTable TC2601    
  NextScan
EndProg

 And here is the live results for CR6 with AM25T, TC2601.

I also have another temperature monitoring system using a CR1000 with AM25T, running a similar program. This system has been operating reliably without any NAN readings.

CR1000 program:

Const Num_T = 7
Dim i
StationName TC2602

Public BattV, PTemp_C, RTempC, Amb, T(Num_T)

Units BattV = Volts
Units Amb, PTemp_C, RTempC, T = °C

DataTable(TC2602,True,-1)
	DataInterval(0,10,Min,10)
	Average(1,BattV,FP2,False)
	Average(1,PTemp_C,FP2,False)
	Average(1,RTempC,FP2,False)
	Average(1,Amb,FP2,False)
	Average(Num_T-1,T(1),FP2,False)
EndTable

BeginProg
	Scan(60,Sec,1,0)
		Battery(BattV)
		PanelTemp(PTemp_C,_60Hz)
		
		BattV = Round(BattV,2)
                PTemp_C = Round(PTemp_C,2)
		
		AM25T(T(1),Num_T,mV2_5C,1,1,TypeK,RTempC,1,2,1,True,0,_60Hz,1,0)
    
                RTempC = Round(RTempC,2)
		For i = 1 To Num_T
		  T(i) = Round(T(i),2)
		Next i
                Amb = T(Num_T)
 
		CallTable TC2602
	NextScan
EndProg

 And it's live results for CR1000 + AM25T are here, TC2602. Since the CR1000 system works reliably, I would appreciate any advice on:

• Possible causes for intermittent NAN readings on CR6
• Whether this could be related to wiring, grounding, excitation timing, or AM25T control ports
• Any recommended changes to the AM25T instruction parameters for CR6

Thank you very much in advance for your assistance.

Best regards,

Does the panel temperature reading of the CR6 also show NAN during that time? If it does, then something is putting too much voltage onto an analog channel or analog ground.

If CR6 panel temperature is fine, I would suspect a loose connection.

No, CR6 panel temperature is fine itself. But when I used it as a refernece temperature at AM25T instruction, it becomes NAN.

Now, all NAN for more than one days, except Battery and CR6 Panel Temp. Last time, when I do a hard restart (power recyle) it went back to normal. Now, I'm going to site to hard restart and check the wiring as well.

Thanks for your replies.

Dear JDavis,

We have carefully checked the wiring and confirmed that everything is in order. We also performed a hard reset the day before yesterday. Since then, CR6 has been recording all readings normally at one-minute intervals up to the present time.

However, we would like to understand the possible cause of the occasional “NaN” readings previously observed for the Reference Temperature of AM25T. We would also appreciate your advice on what measures can be taken to prevent this issue from recurring.

Best regards,

One thing that could cause the NAN reference temperature reading for the AM25T would be a loose ground wire between the AM25T and the CR6. A loose connection could gain or lose connectivity with temperature change. If the reference temperature is NAN, all the thermocouples will read NAN. The reference temperature is used in thermocouple temperature calculation.

Another possible cause for NAN would be a loose power or control connection to the AM25T. If the AM25T did not advance channels, the first and all following measurements would be NAN.

A power cycle of the CR6 does force a full set of backgound calibration. The CR6 does automatic calibration for data logger temperature changes and analog ground voltage offset. Under normal conditions, that process runs about every 6 minutes. If the data logger program is completely full of analog measurements for the given scan rate, background calibration may be disabled. That would show up in the compile results field in the Status table of the CR6.

This post is under review.