Multimeters

To determine resistance, the DMM is equipped with an operational amplifier constant-current source that provides a known current /in the unknown resistor (Fig. 11c). The resultant voltage drop is then measured by the A/D circuit. Some meters provide more accurate resistance measurement by providing leads for the current source that are separate from those used for measurement of the IR drop across the unknown resistor. Since very little current passes through the latter leads, this eliminates any error due to the voltage drop across the measuring leads and connections, which can be significant in the simpler two-lead meter. 

---

A dc/ac volt and ampere multimeter. A true RMS reading meter is optional. 

Star porphyrazines and related multimetal macrocycles 98JHC1013. 

Hand-held multimeters are available with robust, waterproof cases, well-suited for field use. 

In all space heating boiler systems there is a tendency to keep water treatment programs as simple as possible. Ideally, chemical inhibitors should be added in proportion to MU demands, metered water consumption, oxygen content, or other preemptive measurement. More typically, the standard process is to periodically (weekly to monthly) analyze the BW for a few basic control parameters, including measuring the multimetal corrosion inhibitor reserve, and then to merely top-up the inhibitor when the reserve is below the minimum specification. Chemical treatment often is added directly to the BW by hand-pump via a hose cock (bib cock) connection. 

Apart from nitrite and molybdate, silicate is commonly employed in anodic inhibitor programs, although seldom as the primary inhibitor. Both silicates and molybdates provide benefits of synergistic inhibition and also help to reduce corrosion risks through softer waters and multimetal systems. 

The inhibitor-pack is added to the neat glycol for use in multimetal systems. The glycol-inhibitor product is then supplied as 95% glycol and 5% inhibitor. Assuming that the glycol is present at, say, 20% strength in the HW system, the inhibitor concentration in the system is accordingly 1.0% (0.5% actives ), equivalent to 10,000 ppm (5,000 ppm actives ). 

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. 

Although the mechanistic details of this system are not yet clear, it certainly represents a significant step toward the design of Fischer-Tropsch catalysts capable of functioning under mild conditions of temperature and pressure. Furthermore, it lends some credence (vide infra) to the suggestion that multimetal systems may be more useful than monometallic systems for the reductive polymerization of CO. 

Numerous investigators have attempted to control the precursor structure and related solution chemistry effects with varying degrees of success, to influence subsequent processing behavior, such as crystallization tempera-ture.40-42,78,109 110 Particular attention has been given to precursor characteristics such as structural similarity to the desired product and the chemical homogeneity of the precursor species. For multicomponent films, this latter factor is believed to influence the interdiffusional distances associated with the formation of complex crystal structures, such as perovskite compounds. Synthetic approaches have been geared toward the preparation of multimetal species with cation stoichiometry identical to that of the desired crystalline phase.40 42 83 84... 

Hydrometallurgical process, for multimetal waste separation, 21 400 Hydrometallurgical refining, 17 92-93 Hydrometallurgical recycling,... 

Multilevel heat transfer, 13 223 Multimetal waste separation,... 

Multimeters have sockets into which test leads are inserted. Test leads are insulated wires that have banana plugs on one end, for insertion into the sockets, and metal tips on the other end, for contacting the points in the circuit that are being measured. 

Obtain a socket board and multimeter with test leads from your instructor. If not already done, insert the banana plugs on the one end of the test leads into the sockets on the multimeter for volt and ohm measurement. 

Check out the socket board to verify the statements above indicating which sockets are connected internally. To do this, set the multimeter to measure resistance (set to the 2-KQ range) and touch the contact tips of the test leads to any two sockets on the board. If there is internal contact, the resistance measurement will be zero (no resistance). If there is no internal connection, it is an open circuit and the resistance will be infinite. Record the results for each pair of sockets tested. 

---