Electronic Components Datasheet Search |
|
TMP37FS Datasheet(PDF) 11 Page - Analog Devices |
|
TMP37FS Datasheet(HTML) 11 Page - Analog Devices |
11 / 16 page REV. C TMP35/TMP36/TMP37 –11– A Temperature to 4–20 mA Loop Transmitter In many process control applications, 2-wire transmitters are used to convey analog signals through noisy ambient environ- ments. These current transmitters use a “zero-scale” signal current of 4 mA that can be used to power the transmitter’s signal conditioning circuitry. The “full-scale” output signal in these transmitters is 20 mA. A circuit that transmits temperature information in this fashion is illustrated in Figure 10. Using a TMP3x as the temperature sensor, the output current is linearly proportional to the tem- perature of the medium. The entire circuit operates from the 3 V output of the REF193. The REF193 requires no external trimming for two reasons: (1) the REF193’s tight initial output voltage tolerance and (2) the low supply current of TMP3x, the OP193 and the REF193. The entire circuit consumes less than 3 mA from a total budget of 4 mA. The OP193 regulates the output current to satisfy the current summation at the noninverting node of the OP193. A generalized expression for the KCL equation at the OP193’s Pin 3 is given by: IOUT = 1 R 7 × TMP 3x × R3 R1 + VREF × R3 R2 For each of the three temperature sensors, the table below illus- trates the values for each of the components, P1, P2, and R1–R4: Table II. Circuit Element Values for Loop Transmitter Sensor R1( ) P1( )R2( ) P2( )R3( )R4( ) TMP35 97.6 k 5 k 1.58 M 100 k 140 k 56.2 k TMP36 97.6 k 5 k 931 k 50 k 97.6 k 47 k TMP37 97.6 k 5 k 10.5 k 500 84.5 k 8.45 k Illustrated in Figure 9 is a way to convert the output voltage of a TMP3x sensor into a current to be transmitted down a long twisted-pair shielded cable to a ground referenced receiver. The temperature sensors do not possess the capability of high output current operation; thus, a garden variety PNP transistor is used to boost the output current drive of the circuit. As shown in the table, the values of R2 and R3 were chosen to produce an arbi- trary full-scale output current of 2 mA. Lower values for the full-scale current are not recommended. The minimum-scale output current produced by the circuit could be contaminated by nearby ambient magnetic fields operating in the vicinity of the circuit/cable pair. Because of the use of an external transis- tor, the minimum recommended operating voltage for this circuit is 5 V. Note, to minimize the effects of EMI (or RFI), both the circuit’s and the temperature sensor’s supply pins are bypassed with good quality, ceramic capacitors. TWISTED PAIR BELDEN TYPE 9502 OR EQUIVALENT TMP3x R2 R1 4.7k VOUT 0.1 F 2N2907 0.01 F GND VS 5V R3 VOUT SENSOR R2 R3 TMP35 634 634 TMP36 887 887 TMP37 1k 1k Figure 9. A Remote, 2-Wire Boosted Output Current Tem- perature Sensor VOUT VS TMP35 0.1 F GND OP193 0.1 F R1* 24.9k R4 4.99k R5* 1.21M TYPE K THERMO- COUPLE CU CU R2* 102 VOUT 0V – 2.5V R6 100k 5% R3 10M 5% 3.3V < VS < 5.5V COLD JUNCTION CHROMEL ALUMEL ISOTHERMAL BLOCK NOTE: ALL RESISTORS 1% UNLESS OTHERWISE NOTED 0 C T 250 C 7 6 4 3 2 P1 50k Figure 8. A Single-Supply, Type K Thermocouple Signal Conditioning Circuit with Cold-Junction Compensation |
Similar Part No. - TMP37FS |
|
Similar Description - TMP37FS |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |