The IE-251A is a moderately priced intracellular electrometer, complete with current passing capability, incorporating the same basic design as the more costly IE-210. The important features required for low noise, drift free recording from glass microelectrodes have been retained in this lower cost model. The IE-251A is easy to use and an excellent choice for the budget-conscious researcher or student teaching lab.

The IE-251A features a very small active headstage, essentially the same as used with the more costly IE-210. Epoxy-sealed construction affords maximum resistance to saline corrosion. Its small size and low mass permit easy mounting in a micro-positioner. The electrode holder supplied connects directly to the probe input.

The amplifier features include:
• Fixed gains are at x1 and x10.
• Capacity Compensation neutralizes input capacitance up to 50 pF.
• Junction potentials up to ±200 millivolts are nulled with the DC Position control.
• Electrode Test provides convenient electrode resistance check.
• Push button operated Buzz produces oscillations at pipette tip to facilitate cell impalement.
• Convenient Probe Test port permits fast check of amplifier performance.

Current Injection
The injection circuitry of the IE-251A allows simultaneous stimulation and recording through microelectrode resistances up to 1000 megohms in two ranges. Voltages at the Stimulus Input are converted to constant currents applied to the electrode. The steady state and transient components of the current injection artifact are nulled with the DC and transient balance controls. The corrected signal is viewed at the single-ended bridge output. Electrode resistance is read from the DC balance ten-turn dial.

Overdrive Indicators
Two visual indicators call attention to overload conditions:
• Input Overdrive is illuminated whenever the probe input voltage exceeds ±1 V, caused by either excessive current through the microelectrode or an open circuit (open or blocked electrode).
• Current Overdrive warns of excessive voltage (>50 V) applied to the Stimulus Input.

This Intracellular Electrometer is supplied with a probe. An Electrode Holder must be purchased separately based on your glass outer diameter. Also, specify line operating voltage if other than
100-130 VAC.