Manuals+

PASCO Basic Electrometer

Model: ES-9078A

Product Manual

Introduction

The Basic Electrometer is a voltmeter designed for direct measurement of voltage and indirect measurement of current and charge. With a high impedance of 1014 ohms, it is particularly suitable for measuring charge in electrostatic experiments. It offers sensitivity approximately one thousand times greater than a standard goldleaf electroscope, a center-zero meter display indicating charge polarity, and a digits display. The device can measure charges as low as 10-11 coulombs and can output a signal to a PASCO analog interface, enhancing the quantitative nature and ease of electrostatics demonstrations and laboratory work.

The electrometer is powered by four included AA-alkaline batteries, which can be replaced by opening the back casing.

Recommended Equipment

Features

Equipment Diagram

The diagram shows the front panel of the Basic Electrometer (ES-9078A). It features a large analog meter display labeled 'DC VOLTS' with a needle and scale from -10 to +10, and a center zero. To the right of the analog meter is a digital display. Below the analog meter are several controls and ports: a 'VOLTAGE RANGE' selector button, an 'ON/OFF' button, a 'GROUND' port (labeled '7'), a 'SIGNAL INPUT' port (BNC jack, labeled '8'), and a 'ZERO' button (labeled '10'). The diagram also indicates the 'SIGNAL OUTPUT' port (labeled '3') on the side. Numbered callouts point to specific features: 1. Meter display, 2. Digits display, 3. Signal Output port, 4. Voltage range indicators, 5. Voltage range selector button, 6. ON/OFF button, 7. Ground port, 8. Signal Input port, 9. Access to battery compartment (thumbscrews on the back), 10. ZERO button.

Key Features

Included Items

Get the Software

The electrometer can be used with SPARKvue or PASCO Capstone software. For software comparison, visit pasco.com/products/guides/software-comparison.

SPARKvue is available as a free app for Chromebook, iOS, and Android devices. A free trial of SPARKvue and Capstone for Windows and Mac is also offered. Software can be downloaded from pasco.com/downloads or by searching for SPARKvue in your device's app store.

To check for the latest updates:

Operation

Setup

  1. Connect the BNC plug of the signal input cable to the Signal Input port on the electrometer. Align pegs with slots and turn clockwise to secure.
  2. Use the banana plug patch cord to connect the Ground port of the electrometer to an earth ground.
  3. Press the ON/OFF button to power on the electrometer. The displays and a voltage range indicator will light up.
  4. Press the ZERO button to zero the electrometer. The meter LED should align with "0", and the digits display should show 0.0.
  5. Press the Voltage range selector button to choose the desired voltage range (3, 10, 30, or 100 V). The selected range indicates the voltage required for full-scale meter deflection.

Important Points for General Operations

⚠️ IMPORTANT: Always follow these guidelines to prevent personal injury or damage to the device!

Measuring Voltage

The Basic Electrometer functions as an infinite impedance voltmeter. To measure voltage, connect the signal input cable leads to the source, set the voltage range, and read the voltage on the meter or digits display.

Measuring Charge via Induction

This is the preferred method for measuring charge. Use a proof plane and a Faraday ice pail.

Figure 1 Description: The Basic Electrometer is connected to a Faraday ice pail using the Signal Input cable. A proof plane is used to sample charge from an object and then placed inside the ice pail without touching its sides. A charge of equal magnitude and sign is induced on the ice pail's surface, which the electrometer measures.

Using the proof plane and ice pail consistently ensures the capacitance remains the same for all measurements, making the charge on the proof plane directly proportional to the voltage reading.

Measuring Charge via Contact

Charge can also be measured by contact. Touching the inner cylinder of the ice pail with a charged object (like a charged proof plane) results in a negligible change to the electrometer reading, as the total capacitance is only slightly affected.

Charge measurements are indirect, based on the principle that charge is proportional to potential difference (Q = CV). The electrometer readings are always in volts, but the polarity indicates the charge type. For quantitative measurements, use the equation Q = CV, where C is the capacitance of a known capacitor.

Figure 2 Description: This is an ideal schematic of the Basic Electrometer. It is represented as a voltmeter connected in parallel with an internal capacitance, labeled 'CE'. This combination is then connected to an external circuit or object.

The electrometer's internal capacitance (CE) is approximately 27 picofarads (pF). If an external object adds significant capacitance (Cext), the total capacitance becomes Cext + CE, as shown in Figure 3. To accurately calculate charge in such cases, the total capacitance must be determined, unless Cext >> CE.

Figure 3 Description: This schematic illustrates how adding an external capacitance, 'Cext' (representing a charged object or experiment setup), in parallel with the electrometer's internal capacitance 'CE' affects the total capacitance of the system.

Measuring the Capacitance of the Electrometer and Connectors

To measure the precise capacitance of the electrometer and connected instruments:

  1. Obtain a low leakage capacitor (polypropylene or air dielectric) with a known value C (around 30 pF).
  2. Charge the capacitor with a known voltage V (not exceeding 100 V).
  3. Remove the charged capacitor from the power supply, avoiding grounding.
  4. Connect the charged capacitor across the electrometer input leads (or across the pail and shield of the ice pail if including its capacitance).
  5. Record the voltage VE indicated by the electrometer.
  6. Calculate the total capacitance using the equation: CV = (C+CE)VE.

Measuring Current

The Basic Electrometer can be used for indirect current measurements. Connect the electrometer leads across a known resistance in the circuit and measure the voltage. Use Ohm's Law (V = IR) to determine the current. The electrometer's high input impedance has a negligible effect on most circuits, but the voltage drop across the resistor must be within the electrometer's range (100 V maximum).

Alternatively, if connecting across a resistor is inconvenient:

  1. Connect a precision resistor between the electrometer input leads.
  2. Break the circuit and reconnect it in series with the precision resistor, similar to connecting an ammeter.
  3. Measure the voltage across the resistor.
  4. Calculate the current using Ohm's Law.

? NOTE: Ensure the resistance is high enough to measure a voltage drop but low enough not to significantly affect the circuit's current.

Using the Basic Electrometer with an Interface

The Signal Output connector provides an output signal for PASCO analog interfaces (e.g., 850 Universal Interface, UI-5000; 550 Universal Interface, UI-5001). The included interface cable connects directly to an analog port or via a PASPORT port with an Analog Adapter (PS-2158).

Connecting to an interface allows the output signal to be recorded, displayed, and analyzed using PASCO Capstone or SPARKvue software.

? NOTE: Changing the range switch on the electrometer does not affect the output signal's scaling; the software handles scaling.

? TIP: For voltages below 10 V, consider increasing the analog port gain or applying software gain due to the output's limited resolution.

Software Instructions

SPARKvue

  1. Start SPARKvue and click Sensor Data.
  2. Connect your interface to SPARKvue, following the interface manual and online help.
  3. Connect the interface cable from the electrometer's Signal Output port to an analog port on the interface.
  4. In the 'Select measurements for templates' column, select the Properties icon next to the connected channel.
  5. From the sensor options, select 'Electrometer (Basic)' and click OK.
  6. Ensure 'Voltage' is checked in the measurements column. Select 'Graph' from the Displays column to open the Experiment Screen. The graph display will automatically adjust for voltage versus time.
  7. Click Start to begin data collection.

PASCO Capstone

  1. Start Capstone and click Hardware Setup in the Tools palette.
  2. Connect your interface to Capstone, following the interface manual and online help.
  3. Connect the interface cable from the electrometer's Signal Output port to an analog port on the interface.
  4. In the Hardware Setup tool, locate the connected interface image. Click the yellow circle over the port to which the cable is connected and select 'Electrometer' from the list.
  5. Double-click Graph in the Displays palette to create a new graph display.
  6. Click '