Main Output Processor - Standard Curve Buffer; Analog Outputs (Dacs); Auxiliary Analog Inputs (Adcs) - Ametek 7230 Instruction Manual

Chapter 3, TECHNICAL DESCRIPTION

3.3.21 Main Output Processor - Standard Curve Buffer

3.3.22 Analog Outputs (DACs)

3.3.23 Auxiliary Analog Inputs (ADCs)

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non-random signals.
The output processor also operates the standard curve buffer, which is a 100,000
point memory which can be used for storage of selected instrument outputs as
curves, prior to their transfer to a computer via the computer interfaces. In addition
to using this function for the instrument outputs, such as the X channel and Y
channel output signals, it may also be used to store derived outputs and reference
frequency information.
Unlike the fast curve buffer, the available points are split between the number of
outputs to be stored, so that if for example X1 and Y1 outputs were selected, the
maximum recording length would be 50,000 points. Storage operates at rates of up to
1 kSa/s (1 ms per point).
Earlier SIGNAL RECOVERY DSP lock-in amplifiers provided two different types
of analog outputs. Typically there were two outputs driven by DACs that in turn
were connected to the main instrument outputs, and separate auxiliary outputs,
essentially simply programmable DC voltages typically used as control signals for
the experiment. However this architecture created a number of restrictions. In
particular, in the dual modes it was not possible to get both X and Y outputs for both
demodulators when using short time constants, and in some cases it was necessary to
take the analog output from different connectors for different time constant ranges.
This design has been updated and so the 7230 is fitted with four general-purpose
DAC outputs, which can be driven from a variety of output signals, as well as the
traditional programmable "auxiliary DAC" signal, now referred to as the "User
DACs".
Selection of the required outputs for the DACs is made on the Rear Panel web
control panel or via a command sent over one of the interfaces. For each DAC output
there is a selection control, which is used to choose which instrument output will be
sent to the relevant DAC, or to specify that it will be a User DAC. If the latter is
selected then a further control allows the DAC voltage to be set.
Each DAC output is driven by a 16 bit converter operating at a raw update rate of
1 MSa/s, although depending on the output it is generating the actual update rate is
either 1 MSa/s or 1 kSa/s. When used for instrument outputs, full scale corresponds
to ±2.5 V, but the output remains linear to up to ±7.5 V; when used as a User DAC,
the range is ±10.000 V.
The model 7230 incorporates four auxiliary ADC inputs offering a resolution of
1 mV in ±10.000 V. These converters may be used at slow sample rates for digitizing
slowly changing or DC signals which are associated with an experiment, such as
those generated by temperature and pressure transducers, so that they can be
incorporated into ratio calculations or transferred to a controlling computer. They
may also be used in conjunction with the instrument's fast curve buffer to form a
transient recorder operating at sample rates of up to 200 kHz (one channel) or
40 kHz (two channels).