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Dr Andy MacKenzie, University of the West of Scotland

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Dual Channel Differential Electrometer

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FD223a Dual Channel Differential Electrometer

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FD223a Datasheet
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FD223a Instruction Manual
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Electrochemical measurements with ion specific electrodes

  • Dual channel with very high input impedance
  • Separate outputs for Channel A, B and A-B (Differential)
  • Independent DC offset controls
  • Test port
  • Standby mode


  • Measure changes in intracellular ion content electrochemically
  • Stable and drift free
  • Excellent amplification with low noise
  • Driven guard shield for reduced noise and stray capacitance
  • Set probe leakage current


  • Measure intracellular ion concentrations for K+, Ca2+, H+ and other species

FD223A Dual Channel Differential Intracellular Amplifier

The FD223a is a dual differential, high impedance amplifier/electrometer designed specifically for electrochemical measurements using ion specific (K+, Na+, Cl-, etc.) or pH glass microelectrodes.

The instrument is very stable, drift free, and features a built in provision for measuring and adjusting input leakage current. DC levels may be independently adjusted for each probe channel.

The ability to locate the sensing probes directly at the measurement site overcomes the noise introduced by the long cables usually needed to bring the measured potential to the instrument. Signal-driven guards at the probe input maintains the specified high resistance and reduces the stray capacitance of the probes.

Careful design, coupled with quality component selection, particularly in the headstage, results in an excellent amplifier with low noise and wide bandwidth. The FD223a will faithfully reproduce the measured signal.

To reduce the noise and stray capacity even farther the probe housing includes a signal driven guard. A portion of this inner driven shell is exposed at the probe tip allowing a spring shield to be extended over the electrode holder and microelectrode.


Input Impedance > 1015 Ω, shunted by 0.5 pF
Input Capacitance 1 pF, nominal
Leakage Current 75 fA max
Gain 1.000 ± 0.1%
Output Resistance 50 Ω
Input Swing Voltage ±10 V
Rise Time (10 to 90%) 5 µs, small signal
Noise (0.1 Hz to 10 kHz)  
Baseline Stability ±0.1 mV/day
Position Controls Range ±600 mV
Physical Dimensions Case: 8.8 x 21.0 x 17.5 cm (H x W x D)
Probe:12.7 x 65 mm (D x L), 1.8 m cable
Power 90-265 VAC, 50/60 Hz, 10 VA
Probe Handle 6.5 x 65 mm (D x L)
Shipping Weight 2.5 kg
Operating Conditions Equipment is intended to be operated in a controlled laboratory environment. Temperature: 0-40°C; altitude: sea level to 2000 m; relative humidity: 0-95%.


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Replacement probe for FD223A (includes calibration)

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Driven guard shield for FD223AP probe

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Tilting Base. Adjustable to 80 degrees. 5.1"x 0.25"x 2.3" (60 x 130 x 6mm)

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