Hello,
today I repeated the power-on measurement of UR1 on the new LTZ1000 devices:
LTZ7:
start with 24.7 deg C PCB-temperature (NTC populated on PCB) and about 24 deg C room temperature.
I increased the resolution by adding a 400 mV offset so I could use the +/-500mV range and 16 Bits ADC-resolution.
result
start with 523 mV end with 468mV = 55.2 mV difference or 27.6 deg C above 24.7 deg c = 52.3 deg C operating temperature if I calculated it right.
T.C. measurement shows linear T.C. -57 ppb/K up to 40 deg C environment temperature.
LTZ8:
start with 24.6 deg C PCB-temperature
result
start with 533 mV end with 478 mV = 54.5 mV difference or 27.2 deg C above 24.6 deg C = 51.8 deg C operating temperature.
But when I look at the T.C. measurement of LTZ8 it seems that the heater regulation gets instable above 33 deg C environment temperature.
Linear T.C. up to 32 deg C is around -26 ppb/K.
with best regards
Andreas
Hello Andreas,
thank you for these measurements.
I also found 50..52°C on all of my 7 LTZ1000 / 12k/1k references.
I also found similar T.C. figures like you.
My interpretation concerning the 'instability' above 33°C R.T. is, that the visible increase in your last diagram is not necessarily a sign that the oven regulation gets unstable, that is to my opinion an increasing T.C. of higher order, which depends on the degree of compensation. for the -52ppb/K, that anomaly is not visible.
52°C is high enough to have about 38°C R.T. before the margin for the oven control is too small.. All of my newer LTZs can be operated at up to 40°C in that sense, but their individual T.C. compensations, and the resulting reference voltage deviations at higher temperature, limit the usable temperature between 35°C to 40°C.
(At the May meeting, we should have a look on the variety of graphs of my T.C. measurements, difficult to describe here)
That also depends on the thermal packaging. My electronics package heats up 7.5°C above R.T., and I have no additional isolation around the LTZ1000. That means, 40°C R.T. gives 47.5°C inner temperature, and that is barely 5°C regulation margin, so that's the tightest upper limit.
In the end, 12k/1k ~ 52°C oven, is good and safe for each sample, intended for the nominal cal lab of 18..28°C.
(Aren't the 732s specified in a similar manner?)*
Above that, the behavior of each compensated circuit has to be determined.
Frank
*Yes, the 732B is specified for T.C. <= 0.04ppm/K in 15..35°C. Oven temperature is about 45°C