Signal Recovery 7124

The Signal Recovery 7124 Precision Lock-In Amplifier uses a unique analog fiber optic link to interconnect a remote connection unit (RCU), to which the experiment is connected, and a main instrument console. In normal operation there are no digital clock signals within the RCU, and so it can emit no switching noise. This architecture gives an instrument with all the advantages of the latest DSP technology for signal detection, and a powerful processor for easy user operation, as well as low noise performance.

In normal use, the Signal Recovery 7124 Precision Lock-In Amplifier's signal and reference connections are made at the RCU. The signal input can be switched to operate in single ended or differential voltage mode, or in cur mode with a choice of two transimpedance settings. It can also be used to switch between two single-ended voltage signals, for simple sequential measurement, under computer control, of two inputs. In cases where further preamplification is needed then one of the Signal Recovery remote preamplifiers can be used, with its output connected to the Signal Recovery 7124 Precision Lock-In Amplifier's single ended voltage input. This flexible choice of input modes allows the best possible connection to be made to the experiment. The RCU also has both general purpose analog and TTL logic reference inputs, as well as the output for a precision DDS oscillator that generates a sine wave signal of adjustable frequency and amplitude.

The Signal Recovery 7124 Precision Lock-In Amplifier's main console is a compact, benchtop unit with a color display, and keys for operating the instrument controls, accessing diffe menus, and easy entry of numeric values. It receives signals from the RCU module and processes them using powerful DSP algorithms running in a dedicated field programmable gate array (FPGA), supported by a ColdFire processor. The operating frequency range is from 0.5  Hz to 150  kHz, with a main ADC sampling rate and analog output DAC update rate of 1  MHz, which is ideal for use with the available time constants, which go down to 10   µs.

The Main Display is used in normal operation and shows four user-selected instrument controls on the left-hand side and four user-selected outputs, output offset status, and the present reference frequency, on the right. The output display selections include digital and bar-graph displays in a variety of formats. Error information, such as input and output overload, and reference unlock indication, is clearly shown along the top edge of the display, while soft keys along the bottom edge are used for selecting controls and to initiate numerical keypad data entry.

Features and Specifications of the Signal Recovery 7124 Precision Lock-In Amplifier include:

• Extended operating modes:
  • Single Reference Mode:   Harmonic analysis can be performed on harmonics up to 127  x  F
  • Dual Harmonic Mode:
    • Signals at two harmonics of the reference signal can be simultaneously measured
    • Can measure a fundamental frequency and one harmonic of it at the same time
  • Dual Reference mode:
    • Permits measurement of two signals at two unrelated frequencies to be performed simultaneously
    • For example, in an optical experiment the signals passing through two diffe paths can be independently measured if they are modulated at two diffe modulation frequencies
  • Spectral Display:   Allows the spectrum of the signals present at the input to be calculated and displayed, which can help when choosing the reference frequency
  • Tandem Demoldulation Mode:   Allows an amplitude-modulated signal to be first demodulated at a carrier frequency, with the output from this demodulation being processed by a second demodulator running at a lower frequency
• Synchronous Oscillator Output:     An analog sinusoidal signal equivalent to that being used to drive the in-phase demodulator, and available in both internal and external reference modes
• Inputs and Outputs:
  • The 7124 RCU unit has inputs to the signal and reference channel, and an oscillator output
  • It also has an 8-way digital output port for peripheral control
  • The main console provides another oscillator output, auxiliary signal channel input, four auxiliary ADC inputs, and four DAC outputs
  • The DAC outputs can be set to function as analog outputs for the signal measurement (e.g. X, Y, Magnitude, Phase) and/or general purpose programmable analog outputs
• Computer Control:   External control of the unit is via USB, RS232 or Ethernet interfaces, using simple mnemonic-type ASCII commands