HP / Agilent 34401A hidden menu

[Kosmic]

Look at that, my 34401a is reading a PT100 sensor 



This is awesome, thanks a lot guys! 

[iMo]

THERMistor:TYPE {2200,5000,10000} <- Thermistor type (in ohms)

With what b-constant?

[Hydron]

THERMistor:TYPE {2200,5000,10000} <- Thermistor type (in ohms)

With what b-constant?

That is a very good question that's rather poorly answered by HPAK, even for instruments that are meant to natively support temperature measurement. The only info I found was "44000 series" in the 34970A data sheet ("Thermistor 44004, 44007, 44006 series"), which has gotta be these: https://br.omega.com/omegaFiles/temperature/pdf/44000_THERMIS_ELEMENTS.pdf
I think a bit of testing is in order to verify it though (especially checking whether "2200 ohms" is actually 2252); I'm gonna stick with RTDs for now as I have a couple of nice 4W PT100 probes.

@Kosmic - I did indeed crib heavily from the 34970A manual - it actually also has the save/recall stuff, I just didn't get it to work first try as I didn't put a number after *SAV/*RCL. Note that my questions about custom aperture aren't regarding what the SCPI command is (that works similarly to the 34970A, see the end of the first code block where I put my notes), just that it's behaviour is a bit different to the front-panel option.

[iMo]

THERMistor:TYPE {2200,5000,10000} <- Thermistor type (in ohms)

With what b-constant?

.. The only info I found was "44000 series" in the 34970A data sheet ("Thermistor 44004, 44007, 44006 series")

Eeach of the above type from that series has a different beta..
PS: 34410A service manual:
     Probe types: 2.2 kW, 5 kW, 10 kW thermistors; 0.00385%/ºC RTD

[Kosmic]

@Kosmic - I did indeed crib heavily from the 34970A manual - it actually also has the save/recall stuff, I just didn't get it to work first try as I didn't put a number after *SAV/*RCL. Note that my questions about custom aperture aren't regarding what the SCPI command is (that works similarly to the 34970A, see the end of the first code block where I put my notes), just that it's behaviour is a bit different to the front-panel option.

Ok good good. I thought you were looking at the firmware and poking around in SCPI to find the cmds.

[iMo]

FYI - thermistor Beta calculated from the "44000 thermistor series" DS values (Steinhart-Hart):
It fits the common 3975 (2k2 and 5k) and 3695 (10k) betas at 25/85C..

[Hydron]

A quick check with a multi turn trimpot set to the 25C and 85C values (from the table above) for each thermistor option suggests that imo's numbers are bang on - "2.2k" really should be 2252 ohms, and it's probably safe to assume that the 4400x thermistors are indeed the parts intended to be used.

My DMM6500 seems to have the same options (the manual calls out the same 4400x thermistor part numbers), and it applies for the KS 3446x/70 meters too (going by the datasheet at least) - are these three just what DMM manufacturers have standardised on supporting? Lucky for Omega if so!
Is a little disappointing that you don't have the option of custom R and beta on the newer meters at least (though adding that support with a script that would be relatively easy on the DMM6500).

[TizianoHV]

FYI - thermistor Beta calculated from the "44000 thermistor series" DS values (Steinhart-Hart):
It fits the common 3975 (2k2 and 5k) and 3695 (10k) betas at 25/85C..

I confirm that my 34970A uses 10K thermistors with beta=3695 (ask how I know )

[iMo]

I enabled the temperature feature in my meter and tried with 6 random 10k NTCs off my junkbox (3+2+1 different type sets, unknown Betas). The quick test:
a) the 3 were +0.12, +0.2, +0.27C off the LM35 I've been using (+16bit adc), at ambient in open air, aprox 1cm apart, with cold 34401A
b) the 2+1 were +1..+2C off.

Btw. the RTD mode allows to dial in the R0 and alpha.

[alan.bain]

One mystery which I never solved was what is measurement type 9. These are the measurement modes I know about. The firmware definitely references a mode 9. The measurements are classed depending on how the measurement works so e.g. class 0 is DCV like - straight integration over a time window, class 1 is AC like - so sum of squares of measurements over short interval then sqrt (nobody really wants a straight time average of RMS values), class 2 is time/frequency which uses the AD channel 1.

The mystery mode 9 is DCV like.  Maybe I forgot something obvious....or is there something else to discover?

1 DCV  (class 0)
2 ACV (class 1)
3 ohm 2W   (class 0)
4 ohm 4W (class 0)
5 DC A  (class 0)
6 AC A  (class 1)
7 frequency (class 2)
8 period (class 2)
9 unknown ?? (class 0)
10 continuity (class 0)
11 diode (class 0)
12 temp 4 wire RTD (class 0)
13 temp 2 wire RTD (class 0)
14 temp t/c (class 0)
15 temp thermistor (class 0)

[coromonadalix]

can you compare it  with the 34970  brother

[iMo]

Theoretically the mystery "mode 9" could be the Capacitance measurement (see the 34410A).
It works the same as the 2W resistance method - feeding a current into the capacitor, but measuring the ramp (ie. either measuring the time from V1 to V2, or, via a sampling of X DCV samples and calculating the ramp's slope..).
The available 34401A charging currents range is the same as with 34410A.

[iMo]

The question with the Capacitance measurement is how to define the starting point for the measurement, as the charging the capacitor via the 0.5uA to 1mA current source is made in time, and the optimal option is to have the capacitor discharged to zero volts. Then you simply make DCV sampling with a NPLC speed (class 0), till the voltage reaches a max voltage, or, you may do a fixed number of DCV samples within a sweep. Then you calculate the slope of the sampled voltage ramp and from that you get the capacitance. The autoranging from 1nF to 10mF (34410A) would require to alter the constant current value and perhaps NPLC before the ramp sweep to stay in an "optimal" DCV range. The question is how to discharge the capacitor, or how to define the "start" of a sweep. There is a lot of switches inside, they may use a lot of tricks..

PS: for example the const current 0.5uA charges 1nF in 20ms to 10V, while 1mA charges 10mF in 1s to 100mV (all from a discharged capacitor).

[alan.bain]

Sadly examining the CONF? command output on the 34410A (why didn't I think of this sooner) shows that mode 9 isn't capacitance but DC voltage ratio

CONF VOLT:DC:RAT range, res

Capacitance would have been much more useful... now I still need an HP4262/3 :-)

[alan.bain]

Looking at my old notes there's another interesting AC mode on these meters

diag:poke 27,0,1

enables 10kHz AC filter mode (in addition to the usual 3Hz, 20Hz and 200Hz filters) so you can select this with

det:band 10000

This works pretty much like DC measurement off the back of the RMS converter and allows very fast readings to be made (the normal ac modes include a software filter and sum of squares calculation, taking longer for the lower frequency knee). I don't have one of those nice Fluke AC calibrators like the 5200A so I'm not able to check how accurately it works (or test my bench for strength).

This mode doesn't seem persistent over power cycles, although the poke to set it does write NVRAM. 

I'm sort of amused that in the 7-5-2 firmware the flag works by storing 34401 in 0x168c. I didn't notice this at first from a hex listing.

[gerryc89]

Here is the checksum tool posted in the past converted in python.
Gerry

[wkb]

Reviving an old thread:

now that we have this temperature measurement settings menu enabled: how do you set the 34401a for actual temperature measurements? Found myself a K type thermocouple, can set the tc type, units (kelvin, celsius etc)... so now how to actually measure temp?

[Hydron]

To activate the measurement you need to set the "Temp func" to TC - note that a thermocouple needs a reference junction though, so it's a bit less useful than say a RTD, as bench DMMs typically aren't able to simulate this with an internal temperature measurement like most handhelds can. If you have a fixed reference junction e.g. in an ice bath, or by making the thermocouple to meter connections at a known temperature, then you can specify the temperature of that though.

[wkb]

Hm, not sure if I am completely in the clear here: Temp func lives in de G Menu right?

What I am wondering about: how to make the meter go to temp measurements, i.e. how do you make it display celsius or kelvin? Obviously there is no key for that on the frontpanel, but maybe there is a secret key combination?

Or do temp measurements only work over HPIB?

Wilko

[alan.bain]

You can do this from front panel but it's slightly non-obvious.

Menu G 1. TEMP FUNC followed by selection of the probe type should take you into temperature mode (same as CONF:TEMP over SCPI).  You can select units from another of the G menus as well as parameters for the sensor.

[wkb]

Ah, thank you Alain. Non-obvious indeed.

Pictures show it now works. The 6-something degr C indication is before the ambient temp was entered into the meter, the 20-something degr C is after that was done.  A quick test with a hot air soldering station gave me a quite reasonable measurement as compared to the hot air temp setting.

[dreamcat4]

so with SCPI commands... maybe we could make a device to enter the ambient temperature over GPIB / external device? And update it every N seconds?

 

[edit] i suppose what i am really asking is:

well would that be worth doing, would temperature measurements on specific thermocouples actually benefit for the 6.5 digits precision of this meter? rather than using other dedicated equipment

[gray5596]

subscribed

[wkb]

so with SCPI commands... maybe we could make a device to enter the ambient temperature over GPIB / external device? And update it every N seconds?

 

[edit] i suppose what i am really asking is:

well would that be worth doing, would temperature measurements on specific thermocouples actually benefit for the 6.5 digits precision of this meter? rather than using other dedicated equipment

Said thermocouple was, I think, something like €2,50 delivered on my door mat, from China. For some run of the mill, casual, temperature measurements that is hard to beat, assuming of course the DMM itself is already on your bench.

Wilko

[alan.bain]

I'd be interested if anyone could test this, but it seems on my 7-5-2 34401A the thermocouple mode is hard coded to use a 5K thermistor (as in you can change the R25 value via SCPI or front panel but it doesn't seem to have any effect on the output measurement).  I'd suspect this might be a bug (but I can hardly call it a bug in an undocumented feature!). The conversion from value to temp is done via linear interpolation off a table which is more or less uniform in log(R).  It seems to use a beta of around 3850.  The other Rs supported should be 10K and 2K2 (at least that's what the input routine parses).  The attached graph shows the transform function and a linear regression fit to show it's not using a pure beta law.


For quick reference:

SENS:TEMP:TRAN:THER:TYPE {2200,5000,10000}
view as SENS:TEMP:TRAN:THER:TYPE?

I also noticed a strange debug aid for the temp ranges
DIAG:POKE 29,0,1
Tells the meter to skip the conversion from measurement to temperature so displays the raw voltage/resistance (you could of course select a DCV or OHM mode yourself....) DIAG:POKE 29,0,0 turns it off.