Description of hardware used, documentation
Description of hardware used, documentation |
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Show content only (no menu, header)ElectronicsI/O modulesCustom electronics I/O is performed with 3 commercial RS232 cards. The computer communicates with the cards through USB with a USB to RS232 converter.
Temperature sensors10k thermistors are used to sense temperature. Using Wheatstone bridge, with 10k resistors (Rx), 5V excitation voltage.V = E ((R2/(R1+R2)) - Rx/(Rx+R3))Using Wheatstone bridge + resistor R4 in series with bridge. V = E1 ((R2/(R1+R2)) - Rx/(Rx+R3))with E1 = E (R1+R2)//(R3+Rx) / (R4 + (R1+R2)//(R3+Rx)) (R1+R2) // (R3+Rx) = 1/(1/(R2+R3) + 1/(R3+Rx))With E=5V, R1=R2=R3=R4=6.666k : V = 5V (0.5 - Rx/(Rx+10k))With the -10V to -8V voltage range setting on the WTAIN-M, the resolution is 22 uV = 0.18 Ohm on Rx at 0C = 0.4 mK (435 Ohm / C). With the -0.6V to +0.6V voltage range setting on the WTAIN-M, the corresponding temperature range is -10C to +8.5C. Electronics for MountThe original mount electronics were replaced in July 2011 by two EZHR17EN EZstepper circuits (vendor: Allmotion) to improve tracking: the original circuit had unexplained behaviors and somewhat unreliable communication issues with the host computer. The EZstepper also provides more flexibility, and homing can be done without requiring the computer polling limit switch status.
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