Advanced Measurement Technology 273A, Руководство пользователя

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Model 273A Potentiostat/Galvanostat User’s Manual
3.2.6. IR Compensation
There are two modes of IR Compensation, Current Interrupt and Positive Feedback. When
Current Interrupt is enabled, the IR COMP DAC applies the correction voltage derived as a
fraction of the 10.24 V reference. Note that the switch shown beneath the DAC is shown in the
"fixed" reference position, in which the reference input to the DAC is the aforementioned
+10.24V level.
When Positive Feedback IR Compensation is enabled, a fraction of the voltage developed by
the current measurement circuit is fed back as an input to the Control Amplifier through the DAC.
Thus, in this mode, the switch beneath the DAC connects the output of the Current Measurement
circuit to the DAC's reference input. The front-panel E MONITOR output is the electrometer
signal corrected for the amount of iR compensation as shown in the block diagram.
3.2.7. Integration
The integration circuitry on the IR Integrator board provides for analog integration of current for
short timescale coulometry experiments (50 µs
TMB 40 ms). The effective time constant for
measurements ranges from 40 Ns to 40 ms and is controlled by the ITC command. The effective
time constant combines with the current range to determine the full-scale output of the integrator.
The GIGAIN command further affects the effective time constants. See the ITC command in the
Model 273A Remote Programming Command Handbook for more information.
Longer-time scale coulometry experiments (TMB 40 ms) with slowly varying currents may be
performed using SIE 1 to collect current directly followed by numeric integration using either INT
or IINT commands (see the Command Handbook).
3.2.8. Analog to Digital
The Analog-to-Digital conversion section of the instrument has the ability to digitize any one of
four applied signals:
1. The output of the Current Measurement Circuit (I Signal in the block diagram).
2. The I signal after processing by the iR Integrator circuit (Q Signal in the block diagram).
3. The Electrometer Output (E Signal in the block diagram).
4. An Auxiliary A/D Input (Aux A/D Signal in the block diagram).
The A/D section incorporates a low-pass filter for the I signal (only), a computer selectable
gain-of-ten for both the E and I signals, and a computer-selectable additional gain of five for all
four signals (E, I, AUX, and Q). The X2 - X10 buffer's output is applied to a Sample-and-Hold
circuit, which in turn drives a 12 bit A/D Converter that connects to the bus. The A/D Converter,
prior to the gains, has a nominal full-scale range of ± 10 V in MEASURE E, ±2 times full-scale
current in MEASURE I, and ±10 V in AUX A/D. The gain settings made further on are always
relative to these base values.
Both the E and I signals can be offset by the SUPDAC before applying the gains to the signal.
This allows the measurement of small differences on top of large dc values.
3.2.9. OUTPUT and AUX DIGITAL Connector
The OUTPUT provides a voltage proportional to the current or to the computer-calculated
quantities of charge and log current. This is also the signal applied to the Y-axis at the
RECORDER INTERFACE connector.
The AUX DIG I/O interface is used for experimental control and is compatible with TTL as
described in Appendix A.