Teardown : Keithley 2001-TCSCAN CJC card for K2000/2001/2002 - Page 1
Forum section: electronics / testgear

author: TiN
author_rank: Super Contributor
timestamp: October 25, 2016, 08:02:16 am
content: Here I finally present a long delayedteardown article. I had this card for few years already, used from time to time, but never did serious testing of it.IntroSome of DMMs allow expansion with scanner cards and options, useful for automation and production testing setups. One of these cards will be evaluated and studied today in quick teardown. Model 2001-TSCAN from Keithley is 10-channel scanner card, with one of channels dedicated for internal temperature sensor, useful for thermocouples cold-compensation. It also can do 4-wire for resistance.ManualsModel 2001-TCSCAN Instruction manual, Rev.B (with schematics)TeardownPCBA is 6-layer, with lot of thermal mass in inner layers to help equalize temperatures across PCBA. Interesting to note, as even main analog PCBA ofKeithley 2002still only using 4-layers.Connector to main digital board of DMM is Hirose PCN10C-32S-2.54DS or similar. Schematic of the card is publicly available in card's instruction manual, so it's not hard to make own custom scanners for Keithley DMMs.U104 TL7705 is reset supervisor, MICREL 5841YN are simple serial latch drivers for relay control.Input connectionsInput signals and output wiring is connected thru bare wire therminal blocks. All channels HI and LO are isolated, so they has to be routed differentially to test input signals. Scanner card has impact on measurement accuracy due to voltage offsets in signal path. That's why all calibration manuals state not to use scanners for calibration.Output connection (usually rear inputs of DMM) done via OUTA and OUTB pairs. Channel CH1 is tied to U105, which is "Analog Devices AD590MH":http://www.analog.com/media/en/technical-documentation/data-sheets/AD590.pdf in TO-52 hermetic package, thermally coupled to thick copper block.This copper block mounted on bottom side of the board, right under therminal blocks to equalize temperature over the connector pins. Thick copper bar have very good thermal conductivity and lot of thermal mass. With thermal sensor and thermally conductive silicone glue whole block kept at more uniform temperature, to allow proper thermocouple cold-junction compensation.Temperature sensor is laser trimmed to 0.5°C calibration accuracy and has good linearity, typical 0.3°C over full range. It provides +59.23 mVDC at reference temperature of +23.0 °C. Thermal sensor can be calibrated via special procedure and trimmer R151. Details are covered in instruction manual. Sensor is mounted in dead-bug style in round PCB opening to have direct contact with copper block. DMM's own banana jacks don't have cold-junction sensors, so direct thermocouple connection would be compromised by large errors without tedious correction.Copper block dimensions are about 24 x 95 mm with 2 mm thickness. Center section has a cutout for protruding therminal block pins.And finally, comparison to my own xDevs.com X1801 card, featuring low noise isolated power supply for nanovolt preamplifier, such as Keithley 1801 or EM A10.Few commands forGPIB operation with TCSCAN card, same as regular 2000SCAN one.