Hi all,
I was designing LTZ reference based on Linear direct schematics.
It's based with LTC2057 chopper amp, 1:1 output, and planned to have Vishay resistors (but don't have them yet: ((
Assembled one complete board today (as I bought only one LTZ1000A for start) with
available resistors (25-100ppm, best I could get so far).
Also except resistors and zener assembled 4 more boards. Total 3 boards with LTC2057, one with 2xLT1012 and one with 2xLT1097.
4-layer FR4 PCB, gold plated, red solder mask.
Idea behind construction - have zener in own shield box with 2 temperature sensors MAX6610 (one glued to top of LTZ, another on bottom).
Total 3 boards with same batch parts will be installed on bigger "carrier" board with dividers / ratios, low-noise LDO for zeners and monitor chip.
Every VREF board will have thermal shield and whole unit will have one more thermal shield.
So total voltage reference system will have three zener boards with 3 temperature sensors on each plus able to generate 1:2, 1:0.5 and prolly couple
more ratios, plus negative VREF.
I still don't see reason why need 10.00000V or 1.00000V outputs for voltage reference, as there will be DAC system later in unit anyway.
And my meters don't ask for 10 or 1V for calibration either, they want 2.0V and 20V.
Let's take a closer look on first PCB :)
Silk screen on top and bottom around LTZ pins shows areas without copper, so there can be drilled holes if I'll desire to do so later.
Left side (looking on top side) have single opamp and heater control circuit, temperature sensor outputs header.
Right side have input power header (top right) for +15 V, zener opamp and precision resistors.
Zener have force and sense outputs on bottom header.
SMD Capacitors are tantalums and polymer film. I decided to eliminate possibility of piezo effects, so did not use ceramics on board. Will have one test module with ceramic X7R's to try later, as 1206 film caps are expensive.
Also there is MAX6610 temperature sensor (U3) near opamp.
MAX6610 glued to LTZ1000 can on top need to have thin wires routed to header J5.
I wanted try different opamps to find which one have best performance with LTZ1000.
LT1012 version (single-amp variant of industry-known LT1013)
LT1097 version
http://xdevs.com/kb/kx/vref_a01/ver_1097.jp
And chopper amp LTC2057 version (this is being primary at this moment, i'll have 2 more units with LTC2057, two with LTZ1000A and one LTZ1000)
Now bad part ...
Mistake with this board is that U5 power pins are REVERSED. I had component on schematics mirrored vertically, but got distracted and forgot to
. Flip power input nets as well So silly beginner mistake costed one LTC2057 amp:. (
So had to cut pin4 connection, isolate pin7 from PCB pad and bodge jump wire from a cap.
After that board worked fine, and I got magic 7V output!
Now build wonky box shield around zener.
Then put platinum RTD (1000ohm, Honeywell HEL-705) to measure temperature and get reference idea of?? Stable temppoint.
Later will be replaced MAX6610 after I get temperature logs in various conditions.
And close box. Box sides are soldered to power ground on PCB. There are separate grounds as well for zener and everything else, connected only on single point by resistor R9 (0 ohm on right side).
Had done couple thermal camera photos, but forgot to copy those yet. Will post them later.
Wrapped whole thing in insulation foam (K-flex, commonly used in HVAC industry),
and now left overnight powered with 15V from Keithley 2400, and with my cal'd 2001 storing output.
When cold units just powered on, current draw is 43-42mA, drops to 39.x mA in couple minutes and then slowly decreasing, as heater in LTZ1000 warms up.
Higher temperature is - higher voltage output I get.
Measurement / power / DAQ setup for
Voltage Source for Module: Keithley 2400 +15.00 V 55mA
output Voltage Measurement: Keithley 2001 (cal'd by Official Tek Services in beginning of February 2014)
Power supply for Sensors MAX6610: +5.00 V 100mA Max Agilent E3649A
DAQ system for datalogging: Agilent 34970A with mux card 34901A.
Th
PCB stack:
Now need to find and buy low-tempco resistors to make more modules
PS I don't speak chinese, sorry :)
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发表于 2014-3-29 00:23:06
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