Wednesday, January 5, 2011
Weak current College】 【better utilize digital multimeter measurement with 8 tips】.
<br> <br> Tip 1 avoid connection, test, cable and digital multimeter measurement errors caused by line <br> Eliminate the errors of the wiring is the simplest way to zero measurement. For DC voltage or resistance measurement, to select a suitable .measuring range, and then put the probe received together and wait for a measurement - this is the most close to zero input - and then press the zero (null) button. Following the readings will be deducted from the zero measurement results. Zero measurement are .ideal for DC and resistance measurement capabilities. But that this technology is not suitable for AC measurement. AC converters in the range of the lower part can not be good; Agilent34401A digital multimeter analog converter does not require less than 10% of the full degree of .technical indicators. Agilent34410A and 34411A digital multimeter with digital technology, could have been measured with 1% full degree, but it cannot be used to measure the short circuit. <br> <br> Connection <br> If you use different metal connection, .will constitute a thermocouple junction. Thermocouple junction produce with temperature variations in voltage. This voltage is low, but if you are measuring the small voltage, or your system a number of connections, you need to take seriously the problem. You can consider this a .thermocouple junction in the DUT, the relay (multichannel converter) and your digital multimeter. The use of copper-brass-the quantity of this bias is reduced to a minimum. <br> <br> For resistance measurement, you can use the offset .compensation measure any bias voltage, and the deduction of the error. Figure 1 shows the offset compensation survey conducted by the two measurements, the first measurement with a current source, the second measurement without current source. The first reading from the second reading, then .dividing by the known current source current value, you receive the actual resistance values. Since the measurement must take two readings, so the reading speed will decrease, but the accuracy will improve. Offset compensation can be used for two-wire and 4-wire .resistance measurement. <br> <br> <br> <br> Use two measurement bias. The first measurement is the standard ohm measurement; the second is the measurement of thermal electromotive amount of bias. Voltage meter readings are both measured difference divided by .the known current source. <br> <br> Line <br> Four-wire ohms law is the measure most accurate small resistance. In this way will automatically deduct the test line resistance and contact resistance. 4-wire resistance measurement connections are shown .in Figure 2. Use a known current source and the voltage measuring resistors, can calculate the unknown resistance values. A set of additional test line used to hosting resistor to unknown current, above it the voltage can be generated by measuring the voltage sense lines. .There is no current flows through the voltage sense lines, so it will not have a voltage drop. <br> <br> <br> There is no current flows through the voltage sensitive line. Digital multimeter with measured voltage value divided by the known .current to get the value unknown resistance. <br> <br> Internal digital multimeter bias <br> Automatic reset to zero to eliminate the digital multimeter inside the error source. In automatic zeroing is enabled, each time a digital multimeter measurement after the input .signal from the inner disconnect, get a zero reading. And then in the next measurement minus the zero readings. This avoids digital multimeter input circuit in the bias voltage on measurement accuracy. 4-wire measurement auto zero is always enabled, but you can improve .measurement speed and control <br> Auto zero function. When you disable the automatic reset to zero, a digital multimeter with zero reading, and then withdraw it from the subsequent measurement of all. Every time you change the function, quantum or integration time, .a new zero readings. <br> <br> Tip 2 measurement of large resistance <br> Stabilization time effect <br> The capacitor in parallel with the resistors will after the initial connection and the quantum change after stabilization time error. A modern digital .multimeter insert trigger delay, it is used to make measurements to achieve stability in time. The length of the delay depends on the selected function and the quantum. Cable and device of combined electrical capacity less than hundreds of pF, these delays for resistance measurement is .sufficient, but if there is a parallel resistor capacitor, or you log <br> Quantity is greater than 100 k ω resistor, the default delay is not enough. Due to the influence of the RC time constant, stable may take considerable time. Some .precision resistors and multifunction calibrators use parallel of capacitors (1000pF to 100 μ F), and high value resistors with filtering by an internal circuit injected noise current. Due to cable and other equipment of dielectric absorption (invasion), potentially increasing the RC time constant ., and require more stable times. In this case, you may need to be tested before adding trigger delay. <br> <br> Capacitor in the presence of offset compensation <br> If there is a parallel capacitance on resistors, they may want .to turn-off offset compensation. When the offset compensation in the absence of current source for the second reading, it will measure any voltage offset. But if the device has a long stabilization time, it will cause a error in measurement of bias. Digital .multimeter will put the same trigger delay measurement for the bias, in an attempt to avoid the stabilization time. Increase the delay is to make the device fully stable another solution <br> Solutions. <br> <br> High resistance measurement in connection < .br> In your measurement of large resistance, insulation resistance and surface contamination would result in a significant error. You need to take preventive measures to keep high resistance system of "clean". Test lines and fixture on insulating materials and "dirty" surface film .moisture leakage caused by very sensitive. And PTFETeflon insulator (109 Ω), nylon and PVC is relatively poor insulators (1013 G Ω). If you are in a humid conditions measuring 1 M Ω resistor, nylon or PVC insulation leaks to error contribution is .very easy to reach 0.1%. <br> <br> Tip 3 DC bias for AC measurement <br> Many signal contains two AC and DC. Such as asymmetric square wave contains these two ingredients. Many audio signals also contains the DC bias current .of DC offset, the current is used to drive the output transistors. Some circumstances require measurement DC + AC voltage, while others mayOnly AC ingredients. For example, an audio amplifier is the input AC voltage and output AC voltage. <br> Most modern .multimeter in front with a ACRMS converter at DC capacitors. It isolates DC voltage, which allows the measurement of AC value only multimeter. More important is the best for the realization of the multimeter measurement scale AC signal. For example, in measuring power supply AC .ripple, high level of multimeter isolation DC, AC under press components selected range zoom AC signal. <br> For the most accurate measurement of AC + DC, independent measurement of both components. Multimeter is available through the use of suitable measuring range, and .inhibiting AC components integration time, achieve the best possible DC measurement. In AC measurements, to select appropriate AC ingredients range. You can use the following formula to calculate AC + DCRMS value: TrueRMSAC + DC = √ (AC2 + DC2) <br> .New Agilent 34410A and 34411A in AC voltage measurements with other DC capacitors. AC measurement using digital technology, you can get faster stabilization time, and can handle higher crest factor, this is the measurement of pulse train often encounter. In the measurement of pulse, .to ensure that pulse does not contain the frequency is higher than the multimeter bandwidth. 34410A and 34411A measurement of AC signal kHz. If you have a lot of AC components of a lower frequency than 8kHz, then there will be 34410A and 34411A with peak detection .of DC function accurately measure DC and AC components. The higher the frequency of the signal, you can separate measurement AC components, and then use a formula to calculate AC + DC measuring results. <br> <br> <br> <br> .Tip 4-frequency measurement using digital multimeter AC signal <br> Most modern multimeter measuring frequencies as low as the AC signal 20Hz. However, some applications require measurement at lower frequency signals. For this measurement, you need to select a suitable multimeter, and .make appropriate configuration. Please see the following examples: <br> Agilent34410A and 34411A multimeter with digital sampling technology, can be as low as true RMS measurement 3Hz. It through the digital methods in slow filter, stable time to make the best 2.5s, .measurements, you should be aware of: <br> 1. set the correct AC filter is very important. Filter for smoothing true RMS Converter output. In the lower frequency than 20Hz, the correct setting is LOW. In LOW filter settings, by inserting .2.5s delay guarantee multimeter stability. Use the following command sets the low filter. <br> VOLTage: AC: BANDwidthMIN <br> 2. If you know the measured signal of the maximum levels should be set manually on the range, to help speed .measurement. Each time the low-frequency measurement of a long stabilization time will significantly slow down the automatic range. <br> We recommend that you set manual range. <br> DC insulation with a 3.34401A capacitors blocking ACRMS converter measuring DC signal. .Allowing multimeter measurement with the best range AC ingredients. In measurement with high output impedance of the source, to guarantee the stability of every other DC capacitors, the need to ensure that there is plenty of time. Stabilization time from AC signal frequency, but be .affected by any change in the DC signal. <br> <br> There are three measurement TheAgilent3458A ACRMS voltage of method; it's synchronous sampling mode to measure low-1Hz signal. To put the multimeter configured for low-frequency measurements: <br> .1. Select synchronous sampling mode: <br> SETACV: SYNC <br> 2. When you use synchronous sampling mode for ACV and ACDCV function, input signal is DC coupled. The ACV, mathematical methods used in the DC component deducted from reading. .This is important because the combination of AC and DC voltage level can cause overload conditions, even if the AC voltage itself is not overloaded. <br> 3. Select the appropriate measuring range speed measurement, because when you measure low frequency signal, automatic range .characteristics will cause delays. <br> 4. on the waveform sampling, multimeter needs to determine signal cycle. Suspended by ACBAND command to determine the value. If you are not using ACBAND order multimeter may suspend the waveform repeats before. <br> 5 .. synchronous sampling mode-level trigger synchronization signal. But the noise on the input signal could cause false-level trigger, which is not accurate readings. It is important to select the provide reliable trigger source level. For example to avoid the peak sine wave .because the signal change is slower, and the noise was very easy to create false triggering. <br> 6. in order to get accurate readings, to ensure that your surroundings are the electrical "quiet" and use the shield test line. Enable- .level filtering, LFILTERON, to reduce the sensitivity to noise. <br> <br> Configuration can be adopted and 34401A 34410A and 34411A same configuration methods. 34401A <br> With every other DC capacitor voltage analog circuit converts a valid value. It can .measure low-3Hz signal. To achieve the best results, select low-frequency filters, use manual range, and validate various DC bias is stable. When you use a slow filter, insert the 7s delay, thereby ensuring the stability of the multimeter. .<br> <br> Tip 5 selected for digital multimeter sensor for temperature measurement <br> There are four commonly used in digital multimeter measurement temperature sensor: resistance temperature detectors <br> (RTD), Thermistor, IC temperature sensing devices and thermocouple. .They each have their own advantages and disadvantages. <br> Thermistor better sensitivity <br> Thermistor from semiconductor material composition, can provide a very high sensitivity, but they only have a limited temperature range, usually to-80 ° c to 150 ° C .. Thermistor temperature and resistance are nonlinear, so transform algorithm is very complex. Agilent multimeter with standard Hart-<br> Steinhart approximate provide precise transformations, typical resolution 0.08 ° C. <br> <br> With RTD better precision <br> Resistance .temperature detector (RTD) provides resistance and temperature between very precise and highly linear relationship, can measure temperature range of about-200 ° c to 500 ° C. If such modern multimeter Agilent34410A provides standard IEC751 RTD temperature measurement, its sensitivity to 0.0385 Ω / .° C. <br> IC temperature sensing devices and degrees Celsius is the linear relationship between the voltage <br> Many manufacturers can produce a voltage proportional to the degree Celsius and Fahrenheit's probe. These probes are usually use IC temperature sensing device, for example .NationalSemiconductorLM135 series. This class IC devices can cover-50 ° c to + 150 ° C temperature range. You can easily press multimeter displays of probe output calculation temperature. For example 270mV ie equivalent to 27 ° C. <br> <br> Provide .extreme temperature measurement thermocouple <br> Thermocouple measuring-210 ° c to 1100 ° C for a very wide temperature range, its rugged construction can adapt to the harsh environment. And other types of temperature sensors devices are different, thermocouple temperature measurement is relative, .it also requires a for absolute reference junction temperature measurement. But for most applications, add an external reference junction is not reality. We recommend using Agilent34970A data recorder and with built-in reference junction 34901A20 channel multiplexer. 34970A on built-in, applicable to .the common thermocouple temperature transform algorithm. <br> <br> Summary <br> To monitor a temperature, thermistor and 34410A such multimeter is a simple low-cost solution. To get an accurate temperature reading, you should use the RTD. To monitor .multiple temperature or high temperatures, specific data recorder is the best choice. <br> <br> <br> <br> Tip 6 multimeter measurement for in groups <br> Multimeter general usage levels trigger system; to get a reading, you must .meet two trigger condition. Figure 6 shows the 34401A multimeter using two-stage trigger models. Usually the number of hits and trigger is set to 1, receives a triggered a reading. You can also increase the number of sampling, that is to receive a .triggered by N readings. If you keep the 1 hits, and the number increases to N triggered, then every time reading requires the trigger. In both cases, the need to insert trigger delay between the readings. <br> The default configuration of trigger .delay by multimeter, enabling measurement stability, its changes to the range and functionality. Trigger delay can be set manually. It should be noted that this delay is implemented in software, there will be changes in the amount of time describing. In addition, the .measurement time will vary, so it is difficult to use this scenario sample fixed interval signal. Figure 7 shows the use of trigger delay a series of measurements. <br> Figure 8 shows a second trigger models. This is in 34410A, 34411A and use .model 3458A. It allows independent setting trigger delay and the time between samples. In addition, the sample loop (n readings) can be read more quickly and achieve a minimum amount of time changes. Most sample rings in hardware, firmware by at least < .br> Ensure the consistency of the timing. <br> 34410A, 34411A and 3458A configurable to sample readings as quickly as possible, but you can also use the timer. <br> To configure the sudden measurement, delay should be set to trigger after .and before the first reading. Use the timer settings reading room of precise time interval. 34410A and 34411A have front panel data logging capabilities that simplify the configuration of the sudden measurement. <br> <br> <br> <br> <br> .<br> Tip 7 multimeter test peak <br> Multimeter can use DC function sample-frequency signal. Typically the bandwidth limit of 8kHz or lower. Traditionally used analog peak detection circuit capture and maintain peak voltage until A / D circuits capable of measuring the .voltage. This technology provides high-bandwidth, can also be used to capture duration very short spikes. In a multi-channel system also uses this technology, an analog to digital converters and the channel on the peak detectors. This popular technology can very quickly .sampled signal, save its Maxima and minima. <br> In many applications the oscilloscope displays the noise peak energy is smaller. The introduction of noise is typically used by EMI and may mask off the signal of interest - such as the automobile engine will produce .a lot of EMI. Measurement of physical quantities, such as temperature and oil level sensor measurements usually change very slowly. This will be used by the filter and the slower A / D high-frequency noise in the injection. So there's no need to use .high-speed a / D sampling filter output. <br> For the identification and measurement of peak, the multimeter is a very suitable tool. Multimeter provides signal conditioning (gain, attenuation and low-pass filter) and appropriate sampling rate (1kSa / .s to 50kSa / s). Most of the multimeter with built-in arithmetic functions, can be used to determine the minimum and maximum values. To get the maximum reading rate, you might want to post process, because the arithmetic functions might slow down .the reading rate. Increase reading speed of other methods including select small slot, turn-off automatic reset to zero and display. <br> Characterization of signal and peak is identified with a new peak detection characteristics of Agilent 34410A and 34411A multimeter frequently encountered task .. When you monitor a DC signal, you can use sub display shows the peak value and low peak and peak-to-peak. No matter what the time is set by a multimeter, peak detection feature always 50kSa / s sampling, and does not .require mathematical operations. Figure 9 shows up after each reading conventional peak reading update. <br> <br> <br> <br> A reading of an alternative scheme is set to a set of readings in a Group DC reading only returns a peak .measurement results, as shown in Figure 10. <br>> <br> <br> <br> The third scenario is changing the multimeter measurement time slot, for a long time reading. This third method as shown in Figure 11. A longer .measuring returns a peak measurement results. <br> <br> <br> <br> 34410A and 34411A peak detect each 20 μ s sampling time signal. Peak will remain until the next trigger. You can change the measurement time slot time, thus .bringing the spike in long time. Each peak measurement provides the peak-to-peak, peak values and low peak. <br> <br> Tip 8 accessories for multimeter to maximize effectiveness <br> <br> <br> Easier detection < .br> You often want to dual-circuit detection: Watch slide caused probes. 34401A, 34410A and effective reading readings reading so that you can set Agilent34133A precision work easier. This light, and use Agilent patented point probe helps to absorb small slip piercing solder .joint. <br> <br> <br> <br> High-voltage and high current probe <br> High-voltage probe enables you to securely with multimeter measurement under high pressure. Agilent34136A probes by 34401A, 34410A and 34411A use, it .has a fixed input impedance modes (input resistance is 10 M Ω). The probe is 1000: 1 divider, voltmeter measurement capabilities extend to 40kVDC. <br> <br> You can use Agilent34330A shunts (as shown) measure DC and low frequency .AC current (30A, continuous 15A), it is the precision of 0.001 Ω resistor, mounted on epoxy resin sealed plastic box. The flow divider by 1A current output for 1mV. You can tap on the measurement of the current post. Simply put the .wires firmly on the receiving terminal. <br> <br> <br> <br> The probe and manuals and instruments together <br> You often find probes or user manual and time consuming? if you put them in the instrument of "backpack .", you always know their location. Agilent provides can be placed at the top of our common multimeter in two dimensions nylon 34162A suitable for shorter instruments, such as 34410A and 34411A multimeter. 34161A fit 34401A multimeter and 34420A. <br> <br> .<br> <br> For four-wire ohms measurement? <br> Need to purchase additional probes. <br> If you want to make four-wire ohms measurement, you need a second set of test line. 34138A test line applies to .34410A and 34411A. It includes some very tip of the probe and small hoist. Agilent34132A luxury line Kit includes 2 test cable, detachable spring crimping on hook lines, Alligator Clip, stylus and nylon. <br> <br> <br> <br .> The establishment of clean wiring block, the bias to minimize error <br> Agilent34171A digital multimeter input connector block is a set of two connectors, providing connection to all five input easy and reliable way. Terminal with low copper alloy production, different metal connection .of induced voltage reduced to a minimum. It applies to 34401A, 34410A and 34411A. To achieve minimal heat bias voltage, to use all of the connectors the same size of bare copper wire..