THE MULTIMETER

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. 

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. 

Obtain six colored-coded resistors from your instructor and prepare a three-column table in your notebook for recording the color code, the resistance as ascertained from the color code, and the resistance as ascertained by measurement with the multimeter. The color code consists of colored stripes that encircle the cylindrical shape, as shown in Figure 6.14. Also obtain from your instructor a resistor color code wheel (e.g., Radio Shack catalog number 271-1210) and determine the value of all your resistances as ascertained from the color code. For example, if the colors of the stripes left to right as viewed above are red, violet, yellow, and gold, the resistance is 270,000 Q. Record the values in your table. 

Now measure one of your resistances with the multimeter as follows. Insert the wire ends into two sockets on the socket board so that they are not connected internally, such as in sockets FI and F5. (You will have to bend the end wires at about a 90° angle.) Measure the resistance with your multimeter by setting the selector switch to measure resistance and then contacting the lead tips to sockets that make contact with FI and F5, such as G1 and G5. You may have to adjust the selector switch to the proper range for the resistor being measured. Record the value in your table. Measure all the other resistors in the same way. Determine if the accuracy of each, as indicated by either the gold or silver stripes, is correct based on your data and comment on this. 

Next, measure your resistors connected two at a time in series. This means that two of the resistors are connected end to end. When two resistors are connected in this fashion, the total resistance is the sum of the two. To do this, use the socket board and insert the wire ends of one resistor into sockets FI and F5 (as in step 5), for example, so that the ends are not connected internally. Then insert the wire ends of the other resistor into sockets G5 and G9, for example. Since G5 and F5 are connected internally, this connects both resistors in series. Now measure the total resistance by touching the lead tips of the multimeter to sockets HI and H9. Record the individual values of the two resistors, the sum of the two, and the measured value of the sum in another table (four columns) in your notebook. Repeat with several different combinations. Comment on the agreement (or lack thereof) between the calculated and measured values. 

After drying, the filter paper displays a resistance of40-100 kQ, measured with a multimeter by pressing the electrodes into the polypyrrole powder at a distance of 1 cm. The resistance may vary depending on the location of measurement, since the polypyrrole thickness and distribution may vary on the filter paper. Without the polypyrrole, the filter paper has a resistance of at least 10 Q, which in most cases lies beyond the measuring range of the multimeter.Thus it can be shown that the polypyrrole reduces the resistance significantly. 

Electricity you will be surprised how handy it is to have a modern multimeter. Be careful not to overload the multimeter (especially in its resistance and current measuring modes). 

The final hardware device we will discuss is the multimeter (see Figure 1.21). It gets its name from the fact that it is a combination of several different kinds of testing meters, including an ohmmeter, ammeter, and voltmeter. In trained hands, it can help detect the correct operation or failure of several different types of components. 

When measuring circuits, it is very important to have the meter hooked up correctly so that the readings are accurate. Each type of measurement may require that the meter be connected in a different way. In the following paragraphs, we will detail the most commonly used functions of the multimeter and how to make measurements correctly with them. 

To measure resistance, the multimeter must first be set to measure ohms. This is done either through a button on the front or through the selector dial. (Assume for the rest of this book that we are using newer auto-ranging multimeters.) Then the component to be measured must be connected properly between the probes (see the warning and Figure 1.22). The meter will then display the resistance value of the component being measured. 

Do not test resistance on components while they are mounted on a circuit board The multimeter applies a current to the component being tested. That current may also flow to other components on that board, thus damaging them. 

Mixed-metal oxides constitute a significant proportion of electroceramics (e.g., ferroelectrics or superconductors). In addition, electrooptical ceramics such as Pb(LaZrTi)03(PLZT), PbNb2/3Mg1/303(PNM), and Bi4Ti3Ol2 received considerable attention. It may be pointed out that the low-temperature SG route appears to be more suitable for lead containing materials in view of the comparatively more volatile characteristic of lead oxide, which tends to disturb the desired stoichiometry of the multimetal oxide material involving lead, prepared by the MOCVD procedure. 

With the multimeter, measure the open circuit voltage and short circuit current for each cell. Write down the reading for each one. The cells do not have to exactly match each other in voltage and current output. The point is to match the cells so that all of the cells put out voltage and current at or above what your target output is. The lowest single cell output will limit all the others to its output level, so try to match them as closely as possible. 

Next, measure the current output by changing the setting on the multimeter to test current. Again... 

To test the short circuit current simply change the multimeter setting to the current reading or use an ammeter and connect the probes to the same terminals that used to get the voltage reading. 

In a system of this nature there can be many different problems. First, check for the obvious. Are the multimeter probes connected Is the multimeter working properly ... 

If you are sure the system is getting gas, then consider closing the valve in increments on the outlet of the fuel cell to see if that produces any response on the multimeter. Do this until it is dead ended. After a short period of time, if there is no meter response, open up the valve again and move on to another test. 

Procedure (a) Firmly secure a rock salt crystal in between two iron nails on a wire gauze connect both nails to the 220 V or 110 V plug and with the multimeter (caution ). Strongly heat the crystal while observing the multimeter, (b) Make ready an electrical circuit of battery, multimeter, lamp and two... 

Observation (a) The crystal does not conduct electricity at room temperature, but does so when strongly heated. Where the crystal touches the iron nails, one sees light flashes and color changes in the crystal, (b) Molten salts conduct electricity even at a voltage of 6 V the lamp light up, the multimeter shows certain electrical conductivity depending on the distance between the electrodes from each other, (c) Solutions of salt conduct electricity. 

Tip In order to attain a spectacular voltage out of a lemon , two different metal strips could be placed inside the lemon and the voltages measured the juice of the acidic cell serves as an electrolyte solution in this case. If the voltage or the current is too weak to start the motor or the light bulb, the multimeter can be used to measure the electric current. 

Procedure Fill a beaker to half with copper sulfate solution. Fill a clay cell with zinc sulfate solution. Dip metal strips into their respective solutions. The clay cell which contains zinc sulfate solution is placed into the beaker that contains copper sulfate solution. Connect both metal strips to the multimeter finally attach an electric motor into the electric circuit. 

Jim Cassetta (who will soon install his own hydro system and helped me finish this one) drilled the holes in the project box for the toggle switch and TPs. I added small velcro strips to the bottom of the multimeter and the front of the project box so the meter would adhere to the box. This multimeter is designed to hold its own test leads in its lid. I cut a small V in this lid so the wires of the test leads could exit the casing with the lid closed. The test leads then plug into the TPs on the project box, red to red and black to black. This setup permits the owner the option of removing the multimeter from the monitoring station for other duties. Since 1 had extra velcro strips, 1 also added several to one of the bowls of the hydro unit itself. This way, the meter could be stuck to the bowl for any streamside adjustments of the hydro unit s control box. 

Engineers need to measure electron flow when they are designing and testing electrical devices. To perform this measurement operation, they use a tool called a digital multimeter (Figure 13-24). The most common measurements taken with the multimeter are voltage, resistance, and current flow. 

Voltage is the measurement of the force or pressure of the electrons in a pathway. Voltage is commonly referred to as electromotive force and is measured in volts (E). The use of the multimeter to measure voltage is shown in Figure 13-25. 

The ability of a material to resist the flow of electrons is called resistance. Insulators have a high resistance, and good conductors have very little resistance. Resistance is measured in ohms. The Greek letter omega (O) is used by engineers to represent ohms. Figure 13-26 shows how to use the multimeter to measure resistance. 

To measure the flow of electrons along their pathway, the multimeter must be made a part of the pathway or circuit (Figure 13-27). The electrons must pass through the multimeter to be counted, just like the turnstile you walk through when entering a baseball stadium counts the number of fans. 

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