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diff --git a/galvanosyth/manual/manual.tex b/galvanosyth/manual/manual.tex new file mode 100755 index 0000000..a9ea404 --- /dev/null +++ b/galvanosyth/manual/manual.tex @@ -0,0 +1,163 @@ +\documentclass{manual} +\pagenumbering{gobble} + +\title{Dual Low-Current Galvanostat} +\author{Blaise Thompson} + +\begin{document} + +\maketitle + +\vspace*{\fill} +\begin{center} + \includegraphics[width=0.75\linewidth]{../pictures/2018-11-14_104721} +\end{center} +\vspace*{\fill} + +\section{Overview \& Performance} +\pagenumbering{arabic} + +The dual galvanostat is designed to force a small, constant current through an electrolytic cell. +The voltage floats to whatever is needed to maintain that current. +The maximum rated output voltage is 13 V, although in practice the voltage may be able to float several hundred millivolts above 13. +The positive output (red) is guaranteed to be greater than or equal to the negative return (black), in voltage. +Each output of the dual galvanostat is independent, such that the applied voltages may be different. +However, the current set-point of both outputs is the same. + +The dual galvanostat is designed to deliver relatively small currents accurately. +These small current set-points can be crucial when driving particularly slow reactions. +When a galvanostat is set to a current that the reaction of interest cannot support, the galvanostat will naturally swing the output voltage higher. +Often, the galvanostat will end up driving higher-potential undesirable reactions that are more kinetically favorable. +For this reason, this galvanostat has been designed to hold current set-points between 10 $\mu$A and 9.99 mA. + +\autoref{fig:setpoint} shows the agreement between the set current and actual measured current for a constant load of 100 $\Omega$. +Note that the data is displayed on a log-log plot. +The output and setpoint agree to within measurement error for all setpoints above 0.30 mA. +Below this setting, however, the agreement worsens---the measured current consistently overshoots the set current. +The absolute deviation between setpoint and measured current never exceeds 30 $\mu$A. +Please note that the galvanostat is still capable of maintaining these low currents. +The displayed value simply may not correspond to the actual current, so an independent calibration is warranted. + +\autoref{fig:load} shows the applied voltage as a function of load resistance. +In all cases, the set current was 1 mA. +The grey line shows ``ideal'' ohms law behavior. +The saturation of the galvanostat at roughly 13 V can easily be seen. + +\clearpage +\begin{figure} + \includegraphics[width=\linewidth]{../data/2018-11-13/setpoint} + \caption{ + Measured current versus set current. + On this log-log plot, the entire set-point range of 10 $\mu$A to 9.99 mA can clearly be seen. + For both outputs, agreement within measurement error is achieved from 0.30 mA to 9.99 mA. + Unfortunately, both outputs become nonlinear at the lowest setpoints, systematically overshooting the desired current. + For an unknown reason, the agreement is worse for the left-hand output. + All readings were taken with a load of 100 $\Omega$. + } + \label{fig:setpoint} +\end{figure} +\clearpage + +\clearpage +\begin{figure} + \includegraphics[width=\linewidth]{../data/2018-11-14/load} + \caption{ + Measured applied voltage versus load resistance. + All readings were taken at a current set-point of 1 mA. + The ``ideal'' ohms law behavior is represented by the grey diagonal line. + Both outputs saturate at just above 13 V. + } + \label{fig:load} +\end{figure} +\clearpage + +\section{Troubleshooting} + +This section describes calibration and testing of the dual galvanostat. + +When troubleshooting or inspecting the circuit, start by testing each of the power test points. +All power voltages should be measured relative to circuit common at test point 1. +TP2 should be +15 V. +TP5 should be -6 V. +If these are not maintained, check the regulator U1, the inverter U4, and the capacitors C1, C2, C3, C4, \& C5. +C4 and C5 are electrolytic, so they may be the most suspect. + +There are three board-level trimpots that can be adjusted to calibrate the output of the dual galvanostat. +Refer to the schematic and board drawings at the end of this manual to find the location of these trimpots. +They are all three Bourns 3296 series, blue boxes with brass adjusts on the top. + +The first trimpot, RV4, is located near the top of the PCB. +Adjust this trimpot while monitoring the voltage at TP6 relative to circuit common (TP1). +Adjust the external digipot (RV3), and ensure that the voltage at TP6 corresponds directly to the setting of RV3, in mV. +For example, when RV3 reads 999, the voltage at TP6 should be 0.999 V. +Typically it is best to adjust this pot with RV3 set to a large number, since this gives you the most sensitivity in defining the necessary proportionality. + +You may find that TP6 does not respond, or that the response is not proportional to the setting of RV3. +In this case, there may be a problem with the differential amplifier U5 or with the dual buffer U3. +Test the voltage difference between TP3 and TP4, noting that TP3 is always equal to or more positive than TP4. +Like TP6, the voltage between these test points should correspond to the setting of RV3, in mV. +If you are able to confirm correct behavior at TP3 \& TP4 but not at TP6, start by verifying power and replacing U3 and U5. + +Both outputs of the dual galvanostat are driven directly by U6, a dual op-amp. +Each of these has a separate trim pot for the current control, RV1 and RV2. +After verifying correct behavior with at TP6, use a current meter placed across each output to calibrate the control resistors. +Again, it is recommended to adjust these trim pots with RV3 set to a large number. + +\section{Appendix} + +This appendix contains the following: +\begin{ditemize} + \item parts list + \item circuit schematic + \item full board + \item top layer + \item bottom layer +\end{ditemize} + +\clearpage +\subsection{Parts} + +Parts list. +Costs are approximate. +Trivial components like screws, standoffs, feet are not included. + +\begin{tabular}{ + P{\dimexpr 0.02\linewidth-2\tabcolsep}| + p{\dimexpr 0.3\linewidth-2\tabcolsep}| + p{\dimexpr 0.37\linewidth-2\tabcolsep}| + p{\dimexpr 0.15\linewidth-2\tabcolsep}| + P{\dimexpr 0.15\linewidth-2\tabcolsep}} + & name & part & vendor & cost (USD) \\ \hline + 1 & enclosure & CU-3005-A:BUD & UW Stock & 9.00 \\ + 1 & barrel plug, 2.1 mm & 722A:SWITCHCRAFT & UW Stock & 3.00 \\ + 1 & switch & R1966ABLKBLKEFGRN:E-SWITCH & UW Stock & 2.00 \\ + 1 & black banana & 108-0902-001:CINCH & UW Stock & 0.75 \\ + 1 & red banana & 108-0903-001:CINCH & UW Stock & 0.75 \\ \hline + 1 & R1 & resistor, 1 k$\Omega$, 1/4 W & UW Stock & 0.00 \\ + 2 & R2, R3 & resistor, 240 $\Omega$, 1/4 W & UW Stock & 0.00 \\ + 2 & RV1, RV2 & 2K-3296:BOURNS & UW Stock & 3.00 \\ + 1 & RV3 & 3683S-1-103L:BOURNS & UW Stock & 10.00 \\ + 1 & RV4 & 100K-3296:BOURNS & UW Stock & 3.00 \\ \hline + 1 & C1 & capacitor, tantalum, 10 $\mu$F & UW Stock & 0.25 \\ + 1 & C2 & capacitor, tantalum, 330 nF & UW Stock & 0.25 \\ + 1 & C3 & capacitor, tantalum, 100 nF & UW Stock & 0.25 \\ + 2 & C4, C5 & capacitor, electrolytic, 10 $\mu$F & UW Stock & 0.10 \\ \hline + 4 & J0, J1, J2, RV3 (pins) & 22-23-2021:MOLEX & UW Stock & 0.25 \\ + 4 & J0, J1, J2, RV3 (socket) & 22-01-3027:MOLEX & UW Stock & 0.25 \\ \hline + 1 & TP1 & 5012:KEYSTONE & UW Stock & 0.50 \\ + 1 & TP2 & 5010:KEYSTONE & UW Stock & 0.50 \\ + 1 & TP5 & 5011:KEYSTONE & UW Stock & 0.50 \\ + 3 & TP3, TP4, TP6 & 5014:KEYSTONE & UW Stock & 0.50 \\ \hline + 5 & 8 pin DIP socket & 110-93-308-41-001000:MILL-MAX & UW Stock & 1.00 \\ + 1 & U1 & L7815CV:STM & UW Stock & 0.50 \\ + 1 & U4 & LMC7660IN/NOPB:TI & \href{https://www.digikey.com/product-detail/en/texas-instruments/LMC7660IN-NOPB/LMC7660IN-NOPB-ND/32523}{DigiKey} & 1.50 \\ + 1 & U5 & INA105KP:TI & \href{https://www.digikey.com/product-detail/en/texas-instruments/INA105KP/INA105KP-ND/251073}{DigiKey} & 10.00 \\ + 3 & U2, U3, U6 & LM358P:TI & \href{https://www.digikey.com/product-detail/en/texas-instruments/LM358P/296-1395-5-ND/277042}{DigiKey} & 0.50 \\ +\end{tabular} + +\includepdf[angle=-90, fitpaper=true]{../PCB/schematic.pdf} +\includepdf[angle=-90, fitpaper=true]{../PCB/pcb.pdf} +\includepdf[angle=-90, fitpaper=true]{../PCB/front.pdf} +\includepdf[angle=-90, fitpaper=true]{../PCB/back.pdf} + +\end{document} |