ISW 8001 4 DIGIT (8000 COUNTS) PROGRAMMABLE DIGITAL WATTMETER with optional isolated output User Manual INSTRUMENTS ET SYSTEMES ZI des Radars, 12 rue Diderot 91350 GRIGNY FRANCE tel. : 33 (0)1 69 02 31 56 Fax. : 33 (0)1 69 02 08 93 www.instruments-systemes.fr 5/02 ISW 8001 Specifications (+18°C to +28°C) Voltage True RMS measurement Ranges: 50.00 V 150.0 V 500.0 V Resolution: 10 mV, 100 mV, 100 mV Accuracy: 20 Hz-1 kHz : ±(0.4% + 5 digits) DC: ±(0.6% + 5 digits) Input impedance: 1 M // 100 pF Crest Factor: max. 2 at full scale Protection: 750 V peak Current True RMS measurement Ranges: 160.0 mA 1.600 A 16.00 A Resolution: 0.1 mA, 1 mA, 10 mA Accuracy: 20 Hz-1 kHz : ±(0.4% + 5 digits) DC : ±(0.6% + 5 digits) Crest Factor: 4 max. at full scale Protection: 16 A fuse Power Ranges: Resolution: Accuracy: Reactive Power Ranges: Frequency: Resolution: Accuracy: 8.000W 24.00W 80.00W 240.0W 800.0W 2400W 8000W 1 mW, 10 mW, 100 mW, 1W ±(0.5%+ 10 digits) from 20 Hz to 1 kHz ± (0.5% + 10 digits) in DC 8.000VAr 24.00VAr 80.00VAr 240.0VAr 800.0VAr 2400VAr 8000VAr 20-400 Hz 1 mVAr, 10 mVAr, 100 mVAr, 1 VAr ± (2.5 %+ 10 digits) Popwer Factor Display of PF (0 to +1.00) Resolution: ± 0.01 Accuracy (50-60 Hz): ± (2 %+2 digits) (U and I > 1/10 of range) 3 ISW 8001 Isolated Analogue Output : The output is floating with respect to the measuring circuits and digital interface. The cold point is common with the cold point of the probe input. The output shows the instantaneous power. Connection: Safety 4mm banana plugs Output Level: 1Vrms corresponds to 8000 counts/full scale Accuracy: ±2% Polarity: Same as instantaneous power Output Impedance: 10 k Bandwidth: > 1kHz Protection: ± 30V Applied Common Mode Voltage: max. ±30V Current probe input : The input is isolated from the measurement circuits and from the >RS232 interface. The cold point is common with the cold point of the isolated output. Sensitivity : Frequency : Protection : Accuracy : 100mV/A DC and 20Hz to 1kHz ± 30V probe accuracy + 1% Interface : RS232 (3 wires). Xon-Xoff Protocol. Transmission rates 1200 or 9600 Baud Programmability of all functions and ranges. Safety: IEC 1010-1 Cat III 600 V Power Supply: Temperature of Utilisation: 230 V ± 10% , 50-60 Hz, max. 7 W Dimensions: Weight: 240 x 240 x 75 mm (L x W x H) about 1,3 kg General: 4 Digits 25mm high LED Display plus sign Rugged PVC Case with Handle Buzzer indicates Overload 4 10-40 °C RH < 80 % ISW 8001 Safety INSTRUMENTS et SYSTEMES certifies that this instrument has left the factory in perfect working order, both in operation and safety. This instrument has been designed and manufactured with great care to bring the user the best possible safety to the user. If the instrument no longer functions properly or is damaged, it must be immediately disconnected from the ac supply voltage, from the measured circuit voltages and returned for repair. Opening, maintenance, repair and calibration must be carried out by qualified and approved personnel. Warranty Provided it is used under the recommended conditions, this instrument is guaranteed for a two year period against manufacturing defects and component failure. This warranty applies to material and workmanship. The instrument must be shipped back to an agreed repair centre. It will be repaired or replaced without charge. Warranty repairs are made at the discretion of IES. Maintenance Your wattmeter does not need any specific maintenance. Whenever cleaning is necessary, use a soft material. Avoid water or liquids that may penetrate inside. Operation Carefully unpack the instrument and make sure that it was not damaged during transportation. Insert the power cord on the rear of the instrument and connect to the ac supply. Switch power on by means of the power switch located on the rear panel. 5 ISW 8001 6 ISW 8001 Symbols used Indicates the possibility of a dangerous voltage Refer to the user manual Changing a fuse Before you change a fuse, disconnect the instrument from all possible dangerous voltages! The defective fuse must be replaced using a fuse of the same type and value. Two different types of fuses are used: 100 mA time delay fuse on the ac power input circuit (T 100 mA) 16 A semi time delay fuse in the ammeter circuit (16 A M) Selectable Options At start up, the instrument displays first the software version, the transmission rate (- RS option only) of 1200 or 9600 Baud and finally selects the W function (power measurement). Buzzer The buzzer indicates overrange conditions or manipulation errors. It can be switched ON or OFF (toggle) in the following way: Switch OFF the instrument. Hold the VAr key in and switch ON. Release the VAr key when the W function is reached. The new state of the buzzer is kept in memory until you decide to change it. RS 232 Transmission Rate (1200/9600 Baud) Proceed in the same way as for the buzzer but press the cos key before start up. 7 ISW 8001 About Electricity RMS VALUE The RMS (Root Mean Square) value of a signal refers directly to the power. The RMS value of a current which circulates in a resistance equals the value of the DC current which would produce the same heat in the resistance (same power). For this reason, voltage and current measurements are carried out with RMS circuits. The crest factor characterises the shape of a signal. It is the ratio of the peak value to the RMS value (1.414 for a sine wave). The electronic circuits that compute the RMS value are generally sensitive to crest factor. The accuracy of measurements is guaranteed only for moderate crest factors. The max. value of the crest factor is given at full scale. Note that for smaller deviations, the crest factor may be significantly higher. CREST FACTOR In AC circuits, the power is not expressed as the product of the voltage across the load by the current. If voltage and current are sinusoidal, then the power is easily calculated when the phase shift between them is known. Calculation of power parameters becomes complex with non-sinusoidal waveshapes. The ISW 8001 Wattmeter measures the average value of the instantaneous power and remains accurate whatever the shape of the signal, provided it stays inside the specification limits (frequency and crest factor). POWER When reactive elements are inserted in the generator/load circuit, the current and voltage are phase shifted with respect to each other. For : - a sine wave voltage of RMS value V - a sine wave current of RMS value I - a phase shift between voltage and current 8 ISW 8001 we can write the following relations: Apparent Power (Volt Amperes) Active Power (Watts) Reactive Power (Volt Amperes Reactive) VA = V x I W = V x I cos VAr = V x I sin At some moments, voltage and current have the same polarity, at others the signs are unlike. This indicates that some power is either expended in the load, some is returned to the source. When the load is a pure reactance (perfect inductor or capacitor) the power is only reactive and entirely returned to the source. The ISW 8001 Wattmeter measures all kinds of power and displays active or reactive power. For sine waves it can also show the cosine of the phase angle. POWER FACTOR The Power Factor is defined as the ratio : PF = Pr / Pa ( True Power / Apparent Power ) When both current and voltage are sine waves PF = Cos 9 A: ISW 8001 Input Terminals The ISW 8001 Wattmeter uses four input terminals on the front panel: a red plug and a blue plug ( SOURCE) which must be connected to the voltage source. a red plug and a black plug (LOAD) which must be connected to the load. Caution ! : the two red plugs are connected together inside the instrument. The black plug is connected to the blue plug through a low resistance path consisting of the resistive shunt and the protective fuse. No voltage should be applied between the two red plugs and between the black and the blue plugs! Two inputs terminals are mounted on the rear panel : The red plug is the input of the external probe. The black plug is the reference level of the external probe (ground). Output Terminals The isolated output uses a BNC connector (rear panel) to output the power signal. The reference voltage (ground) is common with the current probe input. Function selection Press the appropriate key to select the measuring function. At start up the default measurement function is W (power measurement). The available functions are: W: VAr : PF : V: effective power reactive power Power Factor measurement True RMS voltage (DC + AC). If pure DC is applied, the DC indicator is lit and the polarity displayed. True RMS current (DC + AC). If pure DC is applied, the DC0 indicator is lit and the polarity displayed. 10 ISW 8001 Measuring Ranges Whatever the selected function, voltage and current default to autoranging – e.g. the ranges are automatically switched. There are three ranges for voltage and three ranges for current: 50.00 V, 150.0 V & 500.0 V for the voltage 160.0 mA, 1.6000 A & 16.00 A for the current The selected ranges are indicated by LED’s on the right of the display. To measure voltages To measure voltages, select the V function. The voltage to be measured is applied between the red plug and the black plug (LOAD). The range is automatically selected. If the voltage is pure DC, the DC indicator lights on and the indication of the polarity is activated. A voltage is positive with respect to the black plug is a positive voltage is present on the red plug. No sign is shown for a positive voltage. A negative voltage is indicated by the - sign. 11 ISW 8001 To measure currents The internal circuits are protected by a fuse. If the fuse is blown, it must be replaced with the same type. The fuse is located on the front panel. Make sure that no voltages are applied to the front panel inputs before removing the fuse. The current to be measured is applied between the blue plug (SOURCE) and the black plug (LOAD). The range is automatically selected. If the current is pure DC, the DC indicator lights and the indication of the polarity is activated. A current is positive if it flows from the black plug to the blue plug (this is the polarity of a current delivered by a positive source connected to the red source plug, to a load connected to the LOAD terminals). No sign is shown for positive current. A negative current is indicated by the sign. External current probe 12 ISW 8001 To perform current measurements, the switch located on the rear panel must be in the EXT position (100mV/A). The instrument measures the voltage which appears on the probe input to determine the current flowing through the probe with a sensitivity of 100mV/A. The current shunts remain connected to the black and blue plugs of the front panel, and no voltage must be applied to these terminals. The probe must have a sensitivity of 100mV/a for a direct reading of the current. Probes with different sensitivities may be used, provided a correction is applied to the current. However, no voltage greater than 3Vrms (±4.25Vpeak) should be applied to the input. The input accepts DC or AC voltages. The probe must be connected with the right polarity. A positive voltage applied to the red plug represents a positive current. Reversing the probe changes the sign of the displayed current and power. The use of the external input is indicated by the EXT indicator on the front panel. To measure power The ISW 8001 Wattmeter can measure true power (expressed in W) or the reactive power (expressed in VAr).True power may be measured in DC or AC (inside the bandwidth limits). But reactive power makes sense only AC. It must be done only with sinusoidal values at 50 Hz or 60 Hz. 13 ISW 8001 True power measurement is selected by means of the W key, reactive power by means of the VAr key. The displays shows the power received (or delivered) by the load. It may be slightly smaller (or greater) than the power dissipated by the source because of the small power lost in the voltage divider and the current shunt. True power The true power is generally positive if the generator delivers power to the load. But some loads (batteries, motors) have a strong back e.m.f. and send power back to the source. The wattmeter senses the circulation of the energy in the circuit. If the source delivers energy to the load, the power is considered as positive. If the load sends energy to the source, the value is negative. Reactive power Reactive power is considered as positive for inductive loads and negative for capacitive loads, so, the sign of the displayed values indicates the nature of the load. TWO WATTMETER METHOD 14 ISW 8001 The power on 3 phase network without neutral wire is easily measured with the 2 wattmeter method. This method is also applicable on balanced 3phase network with neutral connection. Generally, only one wattmeter is used with a power switch. Two successive power measurements are necessary with the switch in a different position. The total power is the sum of the two readings. To measure the Power Factor The source and the load are connected as for power measurements. If either voltage or current is too low, the display shows moving signs " -- ". With sine wave voltage and current, the power factor indicates the phase shift between the voltage across the load and the current flowing through a load (cos). Isolated output The isolated output allows the user to observe, with a high degree of safety, the instantaneous power applied to the load with an oscilloscope. The output is isolated from the load and from the RS232 interface. To visualise the instantaneous power, select the WATT function. The output level is calibrated: a level of 1 Vrms corresponds to a full scale display of 2400 or 8000 digits according to the voltage or current range. Note: in power measurement, an auto zero circuit corrects the zero drift. This circuits nulls voltage and current at the input of the multiplier at regular intervals. The result is a zero power during a small amount of time (100 ms). This is visible on the oscilloscope especially at start up (cold circuits) every three seconds. After one minute, the auto zero rate is approximately one auto zero every two minutes. 15 ISW 8001 RS232 Interface (option) To select the transmission rate You have the choice between two transmission rates between the instrument and the computer, 1200 or 9600 Baud. The Baud rate is displayed during a short time at start up. To modify it, press the cos key for a few seconds and switch power on. The new selected rate is displayed and kept in memory until a new change is done. Connection The dialogue between the computer and the wattmeter is accomplished by means of a software protocol (Xon-Xoff). The connection needs only a simple 3 wires cable (Rxd, Txd and signal ground). The connecting cable can be terminated at one end with a 9 pin connector and at the other end with a 9 pin or 25 pin connector, this depends on the PC serial port connector. The following connections should be followed: 25 pin female connector (PC) 9 pin female connector (PC) 9 pin male connector (instrument) 2 3 7 3 (Tx) 2 (Rx) 5 (GND) 3 2 5 To check the communications You can quickly and easily check the connection with the PC_WATT software included with the instrument. First install the software and then switch the instrument off and on to check the transmission rate. If you want to change it see section "To select the transmission rate". 16 ISW 8001 Commands The commands are sent as a string of ascii letters and digits. No special symbol or space should be added. Once sent, the command is executed upon reception of the carriage return character (CR = Hex 13). In terminal mode, this character is transmitted by the ENTER key of the keyboard, along with the Line Feed character which is ignored. Note: the commands may be written either in UPPER or lower case. Some commands will force the instrument to answer. It is the case for the commands: *IDN? : identification VERSION? : software version STATUS? : configuration of the instrument (see § STATUS string) VAL? : measured value. If the command arrives during the measurement cycle, the result will be sent only at the end of the cycle. MA1 : continuous output mode. Each result is sent to the computer. This mode is cleared by the MA0 command. The table of the last page lists all the available commands. Measurement Result The measurement result is transmitted : - - after a VAL? after each measurement if the device is in the auto transmit mode (MA1 command). Ux = 150.1 E +0 Iy = 1.00 E +0 W = 150.1 E +0 ^ ^ ^ | | | ___ W kW Var kVAr PF ACV | | DCV ACI DCI | | | |______ I1 I2 I3 Ix1 | |________ U1 U2 U3 17 ISW 8001 The result is transmitted only at the end of a measurement. If a result query arrives during the measurement cycle, the data will be sent only after a small amount of time (max. 250ms) Automatic Measurements Once the MA1 command has been sent, the measurement data is automatically transmitted after each measurement. The output string includes the instrument status and the value. In this way, the user is continuously informed of the configuration of the instrument. The automatic mode is reset by sending a MA0 command or switching off and on the instrument. Selection of voltage and current ranges When the instrument is manually operated, switching between the different ranges is performed automatically. The choice of the most convenient range is decided by the microprocessor at the end of each measuring cycle. The serial interface gives you the ability to override autoranging and allows the user to select the current or voltage range. At start up, the autorange is always activated. Manual range switching applies to both voltage and current i.e. the selection of a current range will also cause the voltage ranging to change to manual range mode. Two different commands may be used: - the commands MANUAL and AUTORANGE switch from automatic to manual range selection. When switching from autorange to manual, the voltage and current ranges remain unchanged. - the commands of the type SET:Ux and SET:Ix select a voltage or current range ( x = 1, 2 or 3). To disable the front panel The front panel may be disabled in remote operation by means of the command FAV0. The instruments now only responds to the commands from the interface. This mode is cancelled with the command FAV1 or when the instrument is switched off and on again. STATUS String 18 ISW 8001 When the instrument receives a STATUS? command, it sends back a status string which has the following structure: WATT U1 I2 ^ ^ ^ | | |________ | |___________ |______________ current range (I1 I2 I3 Ix1) voltage range (U1 U2 U3) function (WATT Var PF VOLT AMP) The ranges are : U1 : 50V range U2 : 150V range U3 : 500V range I1: 160mA range I2 : 1.6A range I3 : 16A range Ix1 : external probe (100mV/A) Ix2 : external probe (10mV/A) The characters contained in this string are separated with blanks and are easily decoded to inform the user of the operating status. 19 ISW 8001 Table of commands FUNCTION RANGES MODE MISC. WATT VAR VOLT AMP PWF True Power Reactive Power Voltage Current Power Factor SET:U1 SET:U2 SET:U3 SET:I1 SET:I2 SET:I3 MANUAL AUTORANGE Voltage Range : 50V Voltage Range : 150V Voltage Range : 500V Current Range : 0,16A *** Current Range : 1,6A *** Current Range : 16A *** Manual range switching (U & I) Automatic range switching MA1 MA0 Continuous output of data To cancel MA1 mode *IDN? VERSION? STATUS? VAL ? BEEP BEEP1 BEEP0 FAV0 FAV1 Identification query Version query Status query Measured value query Beep once Beeper ON Beeper OFF Disable Front Panel Enable Front Panel *** these commands have no effect if the switch on the rear panel is in the EXT position. 20 ISW 8001 TO USE THE PC_WATT SOFTWARE Installation and de-installation Start Windows®. Insert the PC_WATT floppy disc and execute the file : or a:setup to install the software a:desinst to de-install it The directory ISW8001 will be created during installation. It includes the icon used to start the software. If you want to keep the ability to de-install the software, you must maintain the same structure. 21 ISW 8001 Operating modes Two different operating modes are allowed, the "Terminal" mode and the "Command" mode. In Terminal mode, the computer only monitors the front panel of the wattmeter, which is driven with its own keys. In the Command mode, the front panel is disabled and the instrument is operated with the mouse or the keyboard of the computer. The software starts in Terminal mode. You can modify this mode in the Configuration menu. Starting Connect the interface cable and double click onto the PC_WATT icon to start the software. If the software finds the wattmeter, it directly enters the monitor mode. Else, it opens a communication window where you can modify the transmission speed or the PC serial port to use. Display The Display menu selects the different windows that appear on the screen: - The function/range window which reproduces the front panel of the wattmeter - The communication windows which displays the dialogue between the instrument and the computer Help The help file is opened with the F1 key of the keyboard (dedicated help) or by the ? menu (global help). Measurements The measurements may be accomplished and stored in a file at a desired rate. 22 ISW 8001 The Options menu opens a window where you can define the maximum number of measurements, the time interval between measurements and the structure of the object file. The measurement cycle is initiated with the Start button. The cycle starts as soon as you have typed the name and path of the result file. The result file is a text file with different columns. Each column represents a file selected in the proposed list (function, value, unit, time, date). Note that the value is always selected. The measurement cycle is halted or started at any time with the Start Measurement and Stop Measurement options of the Measure menu. 23