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HP / Agilent 34401A hidden menu
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CBrandin:
I’ve been playing around with the extended temperature settings on the 34401a. To turn on the function temperature feature you must select one of the TEMP FUNCTION options and then press ENTER. Below are all the available menu entries. Note that the entries for T/C TYPE don’t change anything, the only thermocouple type that is supported is N TYPE. Similarly, the entries for THERM TYPE also don’t change anything, the only thermistor type supported in 5 KOHM. I can’t imagine why all those options are there unless there are other memory locations that need to be entered to support them. Maybe somebody who has a version of the 34401a that supports temperature functions (that wasn’t hacked) could try out those options to see if they change anything (dimmog maybe?).

1:TEMP FUNC
   THERMISTOR
   4-WIRE RTD
   2-WIRE RTD
   T/C (Thermocouple)

2:UNITS
   DEGREES C
   DEGREES F
   KELVIN

3:RTD TYPE
   ALPHA-.00385
   ALPHA-.00391

4:RTD Ro
   Set OHMS

5:T/C Type (all types are treated as K TYPE no matter which you choose)
   K TYPE
   N TYPE
   R TYPE
   S TYPE
   T TYPE
   B TYPE
   E TYPE
   J TYPE

6:THERM TYPE (All types are treated as 5 KOHM no matter which you choose)
   2.2 KOHM
   5 KOHM
   10 KOHM

7:JUNCT TEMP (Affects T/C only, usually set to ambient temperature before T/C is mounted)
   Set DEGREES

Many thanks to all those who figured out how to unlock these features!

Chris

Update: These findings are only valid for 7-5-2 firmware.  Later versions appear to support more thermistor and T/C options.

coromonadalix:
as we know the 34401a  has a brother 34970a ... i think there could be remnants of this in the 34401a fw ???
dimmog:

--- Quote from: coromonadalix on October 17, 2023, 12:33:00 am ---as we know the 34401a  has a brother 34970a ... i think there could be remnants of this in the 34401a fw ???

--- End quote ---

I think the 34401A fw was released/developed before 34970A.
iMo:
10k thermistors worked fine here:

https://www.eevblog.com/forum/testgear/hp-agilent-34401a-hidden-menu/msg4662163/#msg4662163
CBrandin:
Strange... I tried both 10K and 5K thermistors and only the 5K ones worked. I even tested it with a 5K resistor to make sure. Maybe it depends on the firmware version you have. Mine is 7-5-2. It makes sense that later they would try out 10K thermistors as they are more common.

I wonder if later firmware versions actually support all the THERM TYPE and T/C TYPE options. My meter was likely built before the 34970a was introduced, and the later firmware versions were produced after.

Chris
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