Non-Contact AC Voltage Probe SP3000, AC Voltage Probe SP9001

Size: px

Start display at page:

Download "Non-Contact AC Voltage Probe SP3000, AC Voltage Probe SP9001"

Camilla Maxwell
5 years ago
Views:

1 Non-Contact AC Voltage Probe SP3000, AC Voltage Probe SP9001 Abstract The Non-Contact AC Voltage Probe SP3000 is a compact probe that can be used with the AC Voltage Probe SP9001 to detect voltage

1 1 Non-Contact AC Voltage Probe SP3000, AC Voltage Probe SP9001 Abstract The Non-Contact AC Voltage Probe SP3000 is a compact probe that can be used with the AC Voltage Probe SP9001 to detect voltage signals from outside cable insulation. It can be connected to a waveform measuring instrument such as a Memory HiCorder or oscilloscope to observe voltage waveforms. This paper introduces these two products features, architecture, and characteristics. Hiroyoshi Ikeda Engineering Division 6, Engineering Department I. Introduction Observing voltage signal waveforms is an effective way to capture data for use in predicting failures or identifying the cause of malfunctions. Until now, it has been necessary to place measurement probes directly in contact with exposed metal parts in order to observe voltage, making measurement difficult in applications where there are no exposed conductive parts, for example on cables and connectors, or where the ends of cables are located deep inside a piece of equipment. Consequently, it is often a timeconsuming task to prepare to carry out such measurements. As automobiles utilize more electronic equipment and production lines introduce more automation, there is growing demand for the ability to observe signals. Hioki developed the SP3000, which makes it easy to measure voltage from outside cable insulation without establishing contact with metal parts, in order to dramatically reduce the number of man-hours associated with signal observation. Appearance of the SP9001 (left) and SP3000 (right). The product was originally intended for utilization in maintenance applications, but it can also be used effectively as a research and development or field testing tool. It can also be used to reverse-engineer devices for which detailed technical drawings or specifications are not available. II. Overview The SP3000 is a probe that can measure voltage from outside a cable s insulation, without making contact with a metal part. The AC Voltage Probe SP9001 is a dedicated probe that is designed specifically for use with the SP3000. Hioki s no-metal-contact voltage measurement technology was first used in the Safety Voltage Sensor PW9020 for the Clamp on Power Logger PW3365, which was launched in The new technology made possible simple safe power measurement [1]. Since the technology at the time was engineered to measure the voltage of commercial power supplies, it was able to measure high voltages but with a frequency band that was limited to commercial power frequencies. The SP3000 was designed to measure voltage waveforms of digital signals output by a range of equipment as well as analog signals output by sensors and other devices. III. Features A. No-metal-contact Voltage Measurement The SP3000 can easily observe voltage signals from outside a cable s insulation thanks to its use of no-metalcontact measurement technology. Its rated measurement voltage is 5 V rms (14.14 V p-p), and its voltage measurement accuracy is ±2.5% rdg. ±1% f.s. No-metal-contact voltage measurement dramatically reduces the number of manhours required in locations that lack a terminal block or make use of waterproof connectors. B. Frequency Characteristics That Suit Measurement Targets The SP3000 delivers stable frequency characteristics across the frequency band from 10 Hz to 100 khz. It can measure voltage fluctuations across the frequency band for measurement targets ranging from machine signals, where

Compact Voltage Probe The tip of the probe has a compact design to allow precise selection of the desired cable in intricate bundles of cables.

2 2 there is high demand for voltage waveform observation, to communications signals used by LIN and other electrical components. However, due to the measurement principles upon which it relies, the sensor is not capable of detecting DC voltages since those signals are not characterized by changes in voltage. C. Compact Voltage Probe The tip of the probe has a compact design to allow precise selection of the desired cable in intricate bundles of cables. In addition, the tip uses a multi-electrode construction in order to minimize the effects of nearby conductors. D. Versatile BNC Output The SP3000 uses molded BNC connectors, which offer excellent durability without any exposed electrodes, for its voltage output terminals. The device can be connected directly to a waveform measuring instrument such as a Memory HiCorder or oscilloscope. In addition, its sensor I/O ratio is 1:1, eliminating the need to convert its output waveforms using a waveform measuring instrument. E. Versatile USB Bus Power The SP3000 uses a USB mini-b connector for its power receptacle, allowing it to operate on USB bus power. In this way, it can be powered directly by any device with a USB terminal. It can also operate on a general-purpose mobile battery, facilitating measurement in locations in the field where it would be difficult to secure a power supply. IV. Measurement Principles and Construction A. Measurement Principles Fig. 1 provides a cross-sectional view of the SP9001, while Fig. 2 provides a structural diagram of the SP9001 s electrodes. Both figures show the device after it has been affixed to a cable. The sensing electrode is positioned opposite the core wire of the cable under measurement at the hook clip on the tip of the probe. Capacitive coupling occurs between this sensing electrode and the core wire of the cable under measurement via the wire s insulation. Due to the capacitive coupling between the core wire and sensing electrode, a current that is proportional to the differential value of change in voltage flows. The constant of proportionality is equal to the coupling capacitance. In other words, (1) applies. Consequently, if the coupling capacitance C is known, the current can in principle be integrated to obtain the voltage value. Fig. 1. Cross-sectional view of the SP9001. Fig. 2. Construction of the SP9001 s electrodes. where i C v t current [A]; coupling capacitance [F]; potential difference [V]; time [s]. dv i = C (1) dt However, in fact the material and thickness of the insulation that comprises the coupling capacitance are unknown parameters. Furthermore, the characteristics vary with temperature-caused changes in permittivity and with clearance. Consequently, it is difficult to calculate the voltage value by computing the coupling capacitance C in advance. The SP3000 addresses this issue by utilizing the coupling capacitance cancelation method, which treats the coupling capacitance C as an unknown parameter. This method creates the potential v 2 on the sensing electrode side of the circuit such that the current i, which is proportional to the coupling capacitance C as shown in (1), approaches zero. As shown in (2), the potential difference v is the difference between the voltage under measurement v 1 and the sensing electrode voltage v 2.

3 3 Fig. 3. SP3000 block diagram. v = (2) v 1 v 2 where v v 1 v 2 potential difference [V]; voltage under measurement [V]; sensing electrode voltage [V]. Based on (1) and (2), the conditions under which the current i approaches zero are those in which the voltage under measurements v 1 and the sensing electrode voltage v 2 have the same amplitude as well as the same phase. Under those conditions, measuring the generated voltage v 2 is equivalent to measuring the voltage in the cable, including phase, even if the coupling capacitance C is unknown. B. Circuit Architecture In keeping with the measurement principles described in Section IV-A above, the coupling capacitance cancelation method requires that the SP9001 s sensing electrode be placed at the same potential as the voltage under measurement. To accomplish this requirement, the SP3000 incorporates a negative feedback circuit architecture, for which Fig. 3 provides a block diagram. A description of that architecture follows. The SP3000 s input consists of the miniscule current that flows to the SP9001 s sensing electrode due to capacitive coupling. This capacitive-coupled current is detected by an I-V conversion circuit with integration functionality. Since output from the I-V conversion circuit is obtained by integrating (1), it resembles the voltage waveform of the measurement target. Gain is applied to the output as necessary, and the result is applied to the I-V converter s reference potential point as a negative feedback voltage. If the negative feedback circuit s loop gain is sufficiently large, the capacitive-coupled current will approach roughly zero, Fig. 4. SP9001 construction. at which point the feedback voltage will be approximately equal to the measurement target s voltage value and phase. The reference potential point to which the negative feedback voltage is applied is located at a floating circuit that includes both the SP9001 guard electrode and sensing electrode shown in Fig. 2. C. Construction and Enclosure The SP9001 incorporates a sensing electrode that detects the capacitive-coupled current that flows between it and the measurement target. The detected capacitivecoupled current is sent via a coaxial cable to the SP3000 s circuitry. All electric circuitry has been consolidated into the SP3000 s enclosure, and the capacitive-coupled current sent from the SP9001 serves as the SP3000 s output voltage after passing through the negative feedback circuit.

4 4 Fig. 5. When clipped to a cable with a diameter of 1 mm. Fig. 6. When clipped to a cable with a diameter of 2.5 mm. Fig. 4 provides a structural diagram of the SP9001, which consists of a sensing electrode, the guard electrode that covers it, a spring that operates the guard electrode, and a cylinder that covers those parts. The guard electrode, cylinder, and coaxial cable s braided shield are all connected so that they remain at the same potential in order to block electric fields from adjacent cables and other sources that could disturb measurement. The hook clip at the tip of the probe can be made to slide open by operating the lever on top of the probe. The tip of the probe incorporates a distinctive low-profile shape. In addition, the design has been optimized so that the clip opens with a minimum amount of movement in order to facilitate measurement of cables with an outer diameter ranging from 1 mm to 2.5 mm routed through confined spaces. Figs. 5 and 6 illustrate the SP9001 when gripping cables with an outer diameter of 1 mm and 2.5 mm, respectively. Fig. 7 provides the construction of the SP3000. The capacitive-coupled current detected by the SP9001 is extremely small in magnitude, making it susceptible to the effects of outside disturbances. Consequently, shield cases cover the input circuitry on the SP3000 s electric circuit board. Since the superposition of the effects of an outside disturbance on the capacitive-coupled current detected by the SP9001 will manifest itself as measurement error, this shielding incorporates a variety of creative design features to ensure its effectiveness. The SP3000 and SP9001 have enclosures made of durable polycarbonate material that is highly resistant to heat, allowing the devices to be used in hot environments. This design reduces the risk of enclosure damage or deformation. Fig. 7. SP3000 construction. Fig. 8. Amplitude vs. frequency characteristics. Fig. 9. Phase vs. frequency characteristics.

5 5 Fig. 10. Example of rectangular wave measurement (top: target waveform, 14 V p-p, 10 Hz rectangular wave; bottom: SP3000 output). Fig. 11. Example of sine wave measurement (top: target waveform, 14 V p-p, 10 Hz sine wave; bottom: SP3000 output). Fig. 12. Example of rectangular wave measurement (top: target waveform, 14 V p-p, 1 khz rectangular wave; bottom: SP3000 output). Fig. 13. Example of sine wave measurement (top: target waveform, 14 V p-p, 1 khz sine wave; bottom: SP3000 output). Fig. 14. Example of rectangular wave measurement (top: target waveform, 14 V p-p, 100 khz rectangular wave; bottom: SP3000 output). Fig. 15. Example of sine wave measurement (top: target waveform, 14 V p-p, 100 khz sine wave; bottom: SP3000 output).

6 6 V. Reference Characteristics Data A. Frequency Characteristics Figs. 8 and 9 illustrate the sensors amplitude vs. frequency and phase vs. frequency characteristics, respectively. Both are flat up to 10 khz, indicating excellent reproducibility of measurement waveforms. Figs. 10 and 11 illustrate the output waveforms obtained from measuring a 14 V p-p, 100 Hz rectangular wave and sine wave, respectively, with the SP3000. Figs. 12 and 13 illustrate the output waveforms obtained by measuring a 14 V p-p, 1 khz rectangular wave and sine wave, respectively, with the SP3000. Figs. 14 and 15 illustrate the output waveforms obtained by measuring a 14 V p-p, 100 khz rectangular wave and sine wave, respectively, with the SP3000. Fig. 16. Voltage linearity. B. Voltage Linearity Fig. 16 illustrates voltage linearity. Linearity is excellent within the range of measurement voltage described in the specification s. C. Temperature Characteristics Fig. 17 illustrates temperature characteristics. The operating temperature range described in the product specifications is 10 C (14 F) to 50 C (122 F), and the characteristics exhibit excellent stability from 20 C ( 4 F) to 60 C (140 F). These results mean that the temperature coefficient of 0.1% rdg./ C (outside the range of 23 C ±5 C [73 F ±9 F]) defined in the specifications is satisfied to a sufficient degree. If the cable under measurement has low temperature resistance, the cable s insulation may be susceptible to temperature effects. When measuring such cables, the capacitive coupling between the SP9001 s sensing electrode and the wire s core may vary significantly, with the result that the effects may exceed the temperature characteristics shown in Fig. 17. Fig. 17. Temperature characteristics. D. Effects of the Wire Type Under Measurement Fig. 18 illustrates the effects of the wire type under measurement. An examination of the effects of the AV 1, AVS 2, and AVSS 3 cables that are ordinarily used in automobiles as well as of the UL1007 and UL1015 cables that are frequently used in a variety of markets indicates a sufficient margin compared with the effects defined in the specifications. 1. Low-voltage cables for automobiles, Specified in JIS C Thin-insulation low-voltage cables for automobiles, Specified in Automotive Standards Organization (JASO) D Super thin-insulation low-voltage cables for automobiles, Specified in JASO D611. Fig. 18. Effects of wire type.

7 7 As described in Section IV-A above, the magnitude of the coupling capacitance does not affect measured values during ideal operation of the SP3000. However, since the SP3000 uses a negative feedback circuit, deviation that is dependent on the magnitude of the loop gain affects measured values. Consequently, the thickness of the cable being measured and the thickness of its insulation are parameters that determine the magnitude of these effects. VI. Conclusion Hioki developed a voltage probe that is capable of easily observing voltage signals from outside a cable s insulation. The company expects the product to find wide use as an option for a range of waveform measuring instruments and to play a useful role in reducing man-hours in the R&D and maintenance fields. Hidehiko Sunohara 4, Koichi Yanagisawa 5, Shin Kasai 5 Reference [1] T. Takahashi, Clamp On Power Logger PW3365/Safety Voltage Sensor PW9020, Hioki Giho (Hioki Technical Notes), vol. 36, no. 1, pp , (Japanese, also available in English). 4. Engineering Division 6, Engineering Department 5. Research & Development Department

AC/DC Current Probe CT6844/CT6845/CT6846

1 Abstract The AC/DC Current Probe CT6844/CT6845/ CT6846 is a clamp on current sensor with a broad frequency range that starts from DC, a broad operating temperature range, and the ability to measure currents