LIA series single board lock-in amplifier

Choose between BV and BVD by the output information required, then select L or H according to the modulation frequency and settling-time requirements. BV models are single-phase instruments with an X output, whereas BVD models provide X, Y and magnitude R, allowing the dual-phase versions to accommodate phase movement without relying on a single aligned channel. L versions cover 5 Hz to 10 kHz and provide time constants from 3 ms to 10 s; H versions cover 50 Hz to 120 kHz with time constants from 300 µs to 1 s. Select L for low-frequency modulation or longer averaging, and H for higher modulation rates or faster response. Confirm that the reference frequency, filter settings and required outputs all fall within the selected variant’s limits.

Yes, but the selected front end and cable capacitance must be treated as part of the measurement design. The differential voltage input covers 3 µV to 1 V full scale, offers AC or DC coupling and presents 1 MΩ in parallel with 4 pF, while the current input is an inverting 100 kV/A transimpedance stage covering 30 pA to 10 µA. Input-noise figures are 12 nV/√Hz for voltage and 0.4 pA/√Hz for current, with 10 pF to 500 pF recommended at the current input. A typical 50 Ω coaxial cable contributes about 100 pF/m, so several metres of cable can consume much of that capacitance allowance. For photodiodes or other current sources, add detector and cable capacitance together, keep the connection short and check the frequency-dependent gain error before finalising the layout.

Start with the input filters, using them to pass the modulation band while limiting unrelated low- and high-frequency components before demodulation. All variants provide 100 Hz, 1 kHz, 10 kHz, 100 kHz and 1 MHz low-pass choices, while the high-pass selections extend from 0.2 Hz to 1 kHz on L versions and from 2 Hz to 10 kHz on H versions. Post-demodulation time constants range from 3 ms to 10 s for L models and from 300 µs to 1 s for H models, with a selectable 6 or 12 dB/octave response. The series specifies up to 80 dB overall dynamic reserve, while the demodulator settings provide 15, 35 or 55 dB. In practice, choose the shortest time constant that meets the required noise bandwidth and verify settling after changing frequency, sensitivity or filter slope.

Treat the unit as a board-level Eurocard rather than a finished desktop instrument. The board measures 160 × 100 × 20 mm, weighs 100 g and uses a 64-pin male DIN 41612 connector with rows a and c for signals, supply and controls. It requires symmetrical rails between ±15 V and ±18 V; budget −60 mA and +100 mA for L variants or −60 mA and +120 mA for H variants. The optional MK-LIA-2 provides a 19-inch front panel and EMI-shielding board backplane, while the SOM-1 module can provide an adjustable reference from 5 Hz to 130 kHz. For multi-channel systems, plan rail capacity per card and maintain controlled grounding, shielding and separation between low-level analogue paths and digital-control wiring.

Sensitivity, time constant and phase can be set using the board switches or through opto-isolated digital inputs. Remote coding uses eight bits for phase, four bits for the time constant and four bits for sensitivity and dynamic-mode selection. A valid low level is −0.8 V to +0.8 V, while a high level may range from +1.8 V to +12 V; typical input current is 1.5 mA at +5 V. Remote bits are logically combined with local switch positions, so the relevant local control should be set to zero when a direct remote code is required. A separate input can disable local controls, while overload and unlocked-reference status outputs allow the host system to identify measurements that may not be valid.

The reference input accepts either a bipolar analogue signal or a TTL-compatible waveform. Bipolar mode covers ±100 mV to ±5 V with a 0 V comparator threshold, while TTL mode accepts −5 V to +10 V and uses a +2 V threshold; the input impedance is 1 MΩ. Reference acquisition takes up to 2 seconds in fast mode or 4 seconds in slow mode, so data capture should wait until the unlocked status has cleared. Phase can be adjusted across 0° to 360°, with 1.4° resolution on L models and on H models below 60 kHz, changing to 2.8° above 60 kHz. Dual-phase variants specify less than 0.1° orthogonality and are appropriate where both in-phase and quadrature information is needed.

The measurement outputs should normally feed a high-impedance acquisition input. Full-scale output is ±10 V with a 2 kΩ load, the output-current limit is ±5 mA and the stated output impedance is 50 Ω; a 50 Ω termination is therefore not compatible with full-scale ±10 V operation. BV variants provide X, while BVD variants provide X, Y and R, with basic accuracy of 2% for X and Y and 4% for R under sinusoidal input conditions. The separate monitor output reaches ±8 V, has 100 Ω impedance and permits ±10 mA. Configure the DAQ for a bipolar ±10 V range with at least the stated 2 kΩ load, and account for the output impedance if additional filtering is added. The offset input can shift the measurement output by ±100% of full scale using a ±10 V control signal.