Multimeters, digital

Some PEM fuel cell performance data were obtained using an electrical resistor to provide a variable load. Two digital multimeters and a shunt resistor were used to measure the voltage and current, so we could calculate the power produced. 

An electrical testing load system was prepared as shown below using two variable resistance potentiometers rated at 0 to 1.0 ohm at 25 watts, a current measuring shunt, and two digital multimeters. 

For the case labeled DC-DC Low-Power, we insert digital multimeters (DMMs) to measure the input and output current. We also connect DMMs directly across the input and output terminals of the converter board to measure input and output voltages. 

Digital voltmeter or digital multimeter, like the one used in Experiment 15... 

Fig. 1.28. Cryoscopy cell, (a) Typical dimensions of the lower section are 260-mm height and 20-mm diameter. The thermistor well is about 27 mm. (b) Cooling apparatus for the cryoscopy cell. The cryoscope slips into the jacketed tube. The jacket is evacuated or partially evacuated to control the cooling rate. Electrical readout is achieved with a digital multimeter or commercial electronics for thermistor thermometers.

Current. Digital multimeters allow the precise measurement of a wide range of currents. Currents are measured by measuring the iR drop across a precision resistor through which the current is passed. 

Components of a home-built IETS spectrometer. DCV=DC voltage ACV = AC voltage DMM = digital multimeter GPIB-IEEE = General Purpose Interface Bus, according to Institute of Electrical and Electronic Engineers Standard 488 [8]. 

Modern multimeters maybe equipped with memory possibilities, and/or interfaces to a personal computer by infrared, IrDA, or serial link, RS-232, or an instrument bus such as IEEE. Modern portable DMMs may have accuracies as good as 0.025%, whereas nowadays bench-top instruments reach accuracies in the single-digit parts per million figures. 

The rapid development of solid-state electronic devices in the last two decades has had a profound effect on measurement capabilities in chemistry and other scientific fields. In this chapter we consider some of the physical aspects of the construction and function of electronic components such as resistors, capacitors, inductors, diodes, and transistors. The integration of these into small operational amplifier circuits is discussed, and various measurement applications are described. The use of these circuit elements in analog-to-digital converters and digital multimeters is emphasized in this chapter, but modern integrated circuits (ICs) have also greatly improved the capabilities of oscilloscopes, frequency counters, and other electronic instruments discussed in Chapter XIX. Finally, the use of potentiometers and bridge circuits, employed in a number of experiments in this text, is covered in the present chapter. 

Electrochemical experiments involved the use of a potentiostat/galvanostat, a current-to-voltage converter, and a universal programmer (PAR Models 173, 176 or 179, and 175). Results were displayed using either an X-Y recorder (Hewlett-Packard 7047A) or a digital oscilloscope (Nicolet 4094 A). The Pd-H versus SCE potentials were measured with both the PAR potentiostat and a digital multimeter (Keithley 175). 

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