6514/E

Programmable Electrometer The Model 6514 Electrometer combines flexible interfacing capabilities with current sensitivity, charge measure­ment capabilities, resolution, and speed that are equal or superior to our earlier electrometers. The Model 6514’s built-in IEEE-488, RS-232, and digital I/O interfaces make it simple to ­configure fully automated, high speed systems for low-level testing. The 5½-digit Model 6514 is designed for applications that demand fast, yet precise measurements of low currents, voltages from high resistance sources, charges, or high resistances. The Model 6514’s exceptional measurement performance comes at an affordable price. While its cost is comparable with that of many high end DMMs, the Model 6514 offers far greater current sensitivity and sig­nificantly lower voltage burden (as low as 20µV) than other instruments can provide. • High speed—up to 1200 readings/second R&D on a Budget The Model 6514 offers the flexibility and sensitivity needed for a wide array of experiments, providing better data far faster than older electrometer designs. Applications include measuring currents from light detectors and other sensors, beam experiments, and measuring resistances using a current source. In addition to use by researchers in areas such as physics, optics, and materials science, the Model 6514’s affordable price makes it an attractive alternative to high end DMMs for low current measurement applications, such as testing resistance and leakage current in switches, relays, and other components. For more information on how the Model 6514 does this, refer to the section titled “Low Voltage Burden.” • Interfaces readily with switches, computers, and component handlers The Model 6514 builds on the features and capabilities of the Keithley electrometers that preceded it. For example, like those instruments, a built-in constant current source simplifies measuring ­resistance. • Cancels voltage and current offsets easily Two analog outputs—a 2V output and a preamp output—are available for recording data with stripchart recorders. • 200TW input impedance on voltage measurements • Charge measurements from 10fC to 20µC ACCESSORIES AVAILABLE Ordering Information LOW LEVEL MEASURE & SOURCE 6514 Programmable Electrometer Accessories Supplied 237-ALG-2 Low Noise Triax Cable, 3-Slot Triax to Alligator Clips, 2m (6.6 ft) Services Available 6514-3Y-EW 1-year factory warranty extended to 3 years from date of shipment C/6514-3Y-ISO 3 (ISO-17025 accredited) calibrations within 3 years of purchase* TRN-LLM-1-C Course: Making Accurate Low-Level Measurements *Not available in all countries CABLES 237-ALG-2 7007-1 7007-2 7009-5 7078-TRX-3   7078-TRX-10 7078-TRX-20 8501-1 8501-2 Low Noise Triax Cable, 3-Slot Triax to Alligator Clips Shielded IEEE-488 Cable, 1m (3.3 ft) Shielded IEEE-488 Cable, 2m (6.6 ft) RS-232 Cable Low Noise Triax Cable, 3-Slot Triax Connectors, 0.9m (3 ft) Low Noise Triax Cable, 3-Slot Triax Connectors, 3m (10 ft) Low Noise Triax Cable, 3-Slot Triax Connectors, 6m (20 ft) Trigger-Link Cable, 1m (3.3 ft) Trigger-Link Cable, 2m (6.6 ft) ADAPTERS 7078-TRX-BNC 3-Lug Triax to BNC Adapter 237-TRX-NG Triax Male-Female Adapter with Guard Disconnected 237-TRX-T 3-Slot Male Triax to Dual 3-Lug Female Triax Tee Adapter 237-TRX-TBC 3-Lug Female Triax Bulkhead Connector (1.1kV rated) 7078-TRX-TBC 3-Lug Female Triax Bulkhead Connector with Cap GPIB Interfaces KPCI-488LPA IEEE-488 Interface/Controller for the PCI Bus KUSB-488B IEEE-488 USB-to-GPIB Interface Adapter RACK MOUNT KITS 4288-1 Single Fixed Rack Mounting Kit 4288-2 Dual Fixed Rack Mounting Kit 1.888.KEITHLEY (U.S. only) www.keithley.com A Greater Measure of Confidence Fast, precise current, charge, voltage, and resistance measurements Fast, precise current, charge, voltage, and resistance measurements 6514 Economical Component Testing Once, electrometers were simply considered too slow to keep up with the high throughput that production test applications demand. The Model 6514 is designed for fast, sensitive measurements, providing speeds up to 1200 readings per second with fast integration or 17 measurements per second with 60Hz line-cycle integration. It offers 10fA resolution on 2nA signals, settling to within 10% of the final value in just 15ms. A normal-mode rejection ratio (NMRR) of 60dB allows making accurate low current measurements, even in the p­ resence of line frequency induced currents, which is a common concern in production floor environments. The instrument’s sensitivity makes it easy to determine the leakage resistance on capacitances up to 10nF or even on ­higher capacitances when a series resistor is used. While the Model 6514 can be easily operated manually using the front panel controls, it can also be externally controlled for automated test applications. Built-in IEEE-488 and RS‑232 interfaces make it possible Electrometer Leakage Resistance RL IL Photodiode (no incident light) ID – + A/D VBURDEN (error current due to VBURDEN) Figure 1. Dark Current Measurement with Burden Voltage Uncorrected 6514 Electrometer RL IL = 0 Photodiode (no incident light) ID – + VBURDEN CAL VOFFSET A/D Total offset voltage = 0 Figure 2. Dark Current Measurement with Burden Voltage Corrected to ­program all instrument functions over the bus through a computer controller. The instrument’s interfaces also simplify integrating external hardware, such as sources, switching systems, or other instruments, into the test system. A digital I/O interface can be used to link the Model 6514 to many popular component handlers for tight systems integration in binning, sorting, and similar applications. These features make the Model 6514 a powerful, low cost tool for systems designed to test optical devices and leakage resistance on low-value capacitors, switches, and other devices, particularly when the test system already includes a voltage source or when the source current/measure voltage technique is used to determine r­ esistance. Low Voltage Burden The Model 6514’s feedback ammeter design minimizes voltage offsets in the input circuitry, which can affect current measurement accuracy. The instrument also allows active cancellation of its input voltage and current offsets, either manually via the front panel controls or over the bus with IEEE-488 commands. Dark Current Measurements When measuring dark currents (Figure 1) from a device such as a photodiode, the ammeter reads the sum of two different currents. The first current is the dark current (I D) generated by the detector with no light falling upon the device (in other words, the signal of interest); the second one is the leakage current (I L) generated by the voltage burden (V BURDEN) appearing at the terminals of the ammeter. In a feedback ammeter, the primary “voltage burden” is the amplifier offset voltage. This leakage current represents an error current. Without the use of cancellation techniques, I L = V BURDEN/R L. Figure 2 illustrates how the Model 6514’s CAL VOFFSET is adjusted to cancel V BURDEN to within the voltage noise level of a few microvolts, so the measured current is only the true dark current (ID) of the photodiode. In a similar manner, offset currents can also be cancelled. Earlier electrometers used an internal numerical correction technique in which the voltage burden was still present, so the measured dark current included the error term I L = V BURDEN/R L. Voltage Burden and Measurement Error Electrometers provide current measurement with lower t­erminal voltage than is possible when making DMM meas­urements. As shown in Figure 3, DMMs measure current using a shunt resistance that develops a voltage (typically 200mV full-range) in the input circuit. This creates a terminal voltage (V BURDEN) of about 200mV, thereby lowering the measured current. Electrometers reduce this terminal v­ oltage by using the feedback ammeter configuration i­llustrated in Figure 1. The Model 6514 lowers this terminal voltage still further—to the level of the voltage noise—by canceling out the small offset voltage that remains, as shown in Figure 2. Any error signals that remain are n­ egligible in comparison to those that can occur when m ­ easuring current with a DMM. 1.888.KEITHLEY (U.S. only) www.keithley.com A Greater Measure of Confidence Fast, precise current, charge, voltage, and resistance measurements Programmable Electrometer LOW LEVEL MEASURE & SOURCE Fast, precise current, charge, voltage, and resistance measurements 6514 6514 Programmable Electrometer VOLTS Accuracy DMM R + – VBURDEN = 200mV at full range VSOURCE Model 6514 specifications A/D Desired Current Reading: Notes 1. When properly zeroed, 5½-digit. Rate: Slow (100ms integration time). I= DMM’s Actual Current Reading: I = VSOURCE R VSOURCE – VBURDEN R Figure 3. Errors Due to Burden Voltage when Measuring with a DMM The example below compares a DMM’s voltage burden errors with the 6514’s. If: VSOURCE = 1V, R = 50kW 1V The desired current reading is: I = = 20µA 50kW Actual Reading (20µA range on DMM): VBURDEN = 200mV I= Refer to Figure 3. 1V – 200mV 800mV = = 16µA = 20% Burden error 50kW 50kW with a DMM 6514 Actual Reading: VBURDEN = 10µV Refer to Figure 2. I= Temperature Coefficient 0°–18°C & 28°–50°C ±(%rdg+counts)/°C 0.003 + 2 0.002 + 1 0.002 + 1 0 .999990V = 19 .9998µA = 0.001% Burden error 50kW with the 6514 DMM Offset Currents Typically, offset currents in DMMs are tens or hundreds of picoamps, which severely limits their low current measuring capabilities compared to the Model 6514 with 3fA input bias current. NMRR: 60dB on 2V, 20V, >55dB on 200V, at 50Hz or 60Hz ±0.1%. CMRR: >120dB at DC, 50Hz or 60Hz. INPUT IMPEDANCE: >200TW in parallel with 20pF,