Intab PC-Logger 3100i Скачать руководство пользователя страница 37 | Manualshive

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Intab PC-Logger 3100i Скачать руководство пользователя страница 37

OPTION : Constant Current Sources

37

OPTION : Constant Current Sources

1 AN

OVERVIEW

Constant Current Sources have their natural use when measuring resistance.
A resistor is in itself passive and does not lend itself to be measured unless
special arrangements are made. It has to be tricked into revealing its value as a
voltage that can be measured and logged.
This voltage has to be proportional to the resistance.

An excursion in time, back to the old school days, may make you remember
”Ohm’s Law”. It states that U=R*I. I.e. ”the voltage across a resistor is the
product of the current through it and its resistance”.
Juggle the letters a bit and you get R=U/I (School maths again).
As current (I) is known and constant it is easily seen that measured voltage is
directly proportional to resistance.

The constant current is almost always set to 0.500mA. I.e. every measured mV
corresponds to 2

Ω

. Insert these values into the formula above and you get:

1mV/0.500mA=
10

-3

/0.5*10

-3

(V/A)=

1/0.5 (V/A) =2

Ω

(V/A=

Ω

)! QED

Below is a schematic diagram of how a constant current source can be put to
work.

R

I

+

U=R*I

-

This method is called ”

four-wire resistance measurement

”.

How to do the practical wiring is shown in a later section in this manual.

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Содержание PC-Logger 3100i

Страница 1: ...How to use PC logger 3100i and accessories INTAB Interface Teknik AB e mail info intab se www intab se...

Страница 2: ......

Страница 3: ...RS 16 6 1 Power 16 6 2 Computer 16 6 3 Connecting Sensors and Transducers 17 7 MISCELLANEOUS 23 7 1 Reset 23 7 2 Program 23 8 TECHNICAL SPECIFICATIONS 24 8 1 Analog Data 24 8 2 Storage Memory 26 8 3 C...

Страница 4: ...Temperature Measurements with Pt 100 Sensors 38 2 DESCRIPTION 39 3 CONNECTING SENSORS 40 3 1 Screw Terminals 40 3 2 Measurement Methods 41 4 TECHNICAL DATA 44 OPTION MODEM PORT 45 1 DATA FORMAT 45 2 C...

Страница 5: ...tops The scope of this manual is to enable the user to correctly connect transducers and use the 3100i off line How the 3100i is handled using our software and a PC is explained in the program manuals...

Страница 6: ...tionally expansion memory Off line measurements should be preceded by the transferral of measurement parameters from the computer to the 3100i These parameters contain among others see program manual...

Страница 7: ...l is then shown every three seconds Try this feature by pressing the intab logo RECORD is selected when you intend to collect data Verify your choice with OK See illustration below Starting a new reco...

Страница 8: ...f how the maximum length of a recording can be calculated from known parameters follows below It is assumed that recordings are made using software supplied by INTAB 3 1 Storage capacity in your compu...

Страница 9: ...is then 6 seconds The formula will be 6 64 000 2 4 48 000 seconds or more than 13 hours The internal memory of the 3100i will only store one recording at a time Starting a new recording will erase th...

Страница 10: ...st take up to about 15 minutes to charge to a point where the 3100i again will be operational Two days of charging should be enough to bring them up to full capacity Some applications require the 3100...

Страница 11: ...source is correctly connected A signal cable consisting of a twisted pair can be very long if the lowest potential of the source is connected to ground via a separate cable The input ranges are set a...

Страница 12: ...nnels have at least 25000 divisions A division is the smallest discernible change in input signal The resolution of an input can be expressed as FSR divided by the no of divisions Two examples a A 10V...

Страница 13: ...ves the signal to 6 A Note that 4 20mA signals are beautifully transformed into correct magnitude and unit by the transform function of the software NOTE that the shunt resistor will overheat if subje...

Страница 14: ...selecting type and range for your application K is the most common type Cold Junction 0 C TYPE mV at 200 C mV at 600 C mV at 1200 C MAX temp C K 8 137 24 902 48 828 1370 N 5 912 20 609 43 836 1300 J 1...

Страница 15: ...terminal area of the analogue board Its temperature is automatically sampled every time a temperature measurement is taken All temperature measurements are thus compensated for the actual temperature...

Страница 16: ...15VDC 2 0V 3 20 28VDC this is an alternative to pin 1 6 2 Computer 3100i connects to a serial port of the computer using the supplied spiral cable The 15 pin D SUB connector has the following pin out...

Страница 17: ...NEL 7 CHANNEL 8 CHANNEL 15 CHANNEL 16 CHANNEL 23 CHANNEL 24 U I 13 14 15 16 U I 12 10 11 U I 21 22 23 24 9 CHANNEL 21 CHANNEL 22 CHANNEL 13 CHANNEL 14 CHANNEL 5 CHANNEL 6 GND GND U I 17 18 19 20 CHANN...

Страница 18: ...al connection to signal ground Input block diagram Differential channels measure as the name implies the difference in voltage between the and input in relation to signal ground Another way of saying...

Страница 19: ...ur signal paths To maintain the validity of your measurements you have to take the common mode range into account Common mode range is 10V for most ranges LOGGED SIGNAL CHANNEL GND ref MAX 10V COMMON...

Страница 20: ...ombined but you have to make sure that your ground leads don t carry any current or connect to the same point from two directions Ground leads that carry current will at best ruin your measurements At...

Страница 21: ...re must also be taken so that other equipment don t introduce common modes outside the permitted range Least problems should arise if the 3100i is inserted as near the most negative end of the loop as...

Страница 22: ...ethods can be combined if care is taken to avoid ground loops 1 Signals with Common ground reference 1 2 GND DIFF Connect 3100i signal GND to system ground Connect sensors Place switch in position DIF...

Страница 23: ...oftware Please consult your software manual for details Bootable files have the extension LDM The Intab PC logger software automatically selects the correct one if there are several present on the dis...

Страница 24: ...3 Time Base X tal reference Uncertainty 20ppm at 20 C Stability 50ppm 20 C to 60 C 8 1 4 Inputs 8 16 or 24 differential inputs Impedance Overvoltage protection Min 400 k 30V continuous Higher voltages...

Страница 25: ...ross the input by using the on board switch see 5 2 NOTE Max allowed current through shunt is 80mA 8 1 6 Divisions Min 25000 divisions 8 1 7 Resolution Examples Range Resolution approx 10V 0 4mV 1000m...

Страница 26: ...on 0 5 C 8 1 9 Common Mode Common mode range CMR min 5V at 10V FSR min 10V other ranges min 80dB 8 2 Storage Memory Sizes 0k Bytes only for on line recordings 64k Bytes optional 64k 512k Bytes optiona...

Страница 27: ...ntinuously trickle charged Capacity Min 2 hours of operation with fully charged accumulators 8 5 2 Charger Mains Adapter Voltage 12 15VDC Current Min 500 mA 8 6 Mechanical specifications Width 165mm L...

Страница 28: ...28 INTAB Interface Teknik AB...

Страница 29: ...card has the following I O s 4 digital outputs relays 8 digital inputs 6 of which are used as inputs to the counters 1 1 Digital Outputs Four digital outputs in the form of relay contact closures are...

Страница 30: ...l input status is reflected in channel 31 The binary sum of active inputs are presented with DI1 as LSB 1 2 1 Opto isolated inputs The Opto isolated inputs DI1 DI8 are used to detect high level 10V si...

Страница 31: ...volume They are therefore an excellent example of how the counters can be used to measure flow Counter values are presented in channels 25 through 30 2 1 Reset mode Reset mode will reset or zero the c...

Страница 32: ...pter is able to supply and never more than 500mA Terminal configuration is shown in the illustration below DI 8b DI 8a DO 4b DO 4a DO 3b DO 3a DO 2b DO 2a DI 7b DI 7a DI 6b DI 6a DI 5b DI 5a DO 1b DO...

Страница 33: ...ssible on DO1a b DO4a b see figure DIGITAL OUTPUTS RELAY SPST DO a DO b Switching Capability Power 30W 50VA Voltage 45V AC DC Current 1 25A AC DC N B No voltage above 45V may be applied to any part of...

Страница 34: ...at mechanical contacts always bounce when brought together This bouncing will unless filtered result in a burst rather than one pulse VO GND OR DI b DI a PULSE MAX 24V OPTO ISOLATION ANY POLARITY DI a...

Страница 35: ...olated Inputs No of inputs Low level High level Max input voltage Impedance Input current Max frequency 8 Max 4V Min 8V 30V Min 1k Ohms Max 30mA at 30V in Min 30kHz at duty cycle50 4 2 2 TTL compatibl...

Страница 36: ...INTAB Interface Teknik AB 4 3 Auxiliary Power 4 3 1 for Opto Couplers Voltage mains adapter output max 15V Current mains adapter rating 300mA or max 200mA 4 3 2 for TTL Inputs Voltage 4 6V Impedance...

Страница 37: ...that U R I I e the voltage across a resistor is the product of the current through it and its resistance Juggle the letters a bit and you get R U I School maths again As current I is known and consta...

Страница 38: ...noted In four wire techniques total uncertainty is the sum of 3100i analog channel uncertainty and constant current uncertainty The analog inputs have an uncertainty of 300ppm Using the 100mV range a...

Страница 39: ...es between 80ms and 100ms to sample The maximum time the constant current is flowing is actually only this long Therefore it never contributes to any self heating of the sensor What are the implicatio...

Страница 40: ...ected to sensors 8 16 24 21 22 23 13 14 15 5 6 7 20 12 4 2 3 10 11 18 19 17 9 1 The constant current comes out of the terminal whenever the corresponding channel is sampled It should pass through the...

Страница 41: ...lace in some applications A three wire version of the five wire method can also be employed where the demand for accuracy is small Three wire resistance measuring where the three wire device is part o...

Страница 42: ...00 sensors It can of course be expanded to up to 24 sensors You realise of course that these can be combined with other sensors and transducers that don t require current sources Analogue board Consta...

Страница 43: ...veloped by a similar current source across a reference resistor R2 The lead return resistance is with this method elegantly compensated for as it is included in both the minus and plus signal and thus...

Страница 44: ...e contribute to a considerable measurement error This is how you go about connecting the three wires Compare this to the five wire method 0 500mA Constant Current 0 500mA Constant Current I R1 Pt 100...

Страница 45: ...FORMAT The serial data format between the 3100i and a modem is 1 Start Bit 8 Data Bits 1 Stop Bit No Parity 2 CONNECTOR STANDARD The connections adhere to a subset of the RS 232C standard The connecto...

Страница 46: ...grams how many rings that must arrive before the call is answered The commands have the following default settings BPA_0226 LDM or later INITANSWER ANSWER RING DIAL ATE0 ATA 3 Has no initial settings...

Страница 47: ...choice have to be set up to report DCE line speed and error correction method xxx arbitrary letters The following two types of messages are accepted CONNECT 14400 No error correction CONNECT 14400 xxx...

Страница 48: ...tachable 17 DIAL 46 DIFF 21 22 differential 18 DIFFERENTIAL 11 digital I O 29 digital inputs 30 digital outputs 33 division 12 downloading 6 D SUB 16 DTE connector 45 duration 8 E E 12 endless 9 erase...

Страница 49: ...ding time 9 relay coils 29 relay outputs 29 Reset mode 31 resistance 37 resolution 13 retain data 9 RING 46 RS 232 26 RTC 5 RTD 38 S S 12 14 screw terminal 15 screw terminals 17 self heating 39 shunt...

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