functional block diagram rev. b information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a thermocouple conditioner and setpoint controller ad596*/ad597* features low cost operates with type j (ad596) or type k (ad597) thermocouples built-in ice point compensation temperature proportional operation C 10 mv/ 8 c temperature setpoint operation C on/off programmable switching hysteresis high impedance differential input general description the ad596/ad597 is a monolithic temperature setpoint con- troller that has been optimized for use at elevated temperatures such as those found in oven control applications. the device cold junction compensates and amplifies a type j or k thermo- couple input to derive an internal signal proportional to tem- pera ture. the internal signal is then compared with an externally applied setpoint voltage to yield a low impedance switched output voltage. dead-band or switching hysteresis can be programmed using a single external resistor. alternately, the ad596/ad597 can be configured to provide a voltage output (10 mv/ c) directly from a type j or k thermocouple signal. it can also be used as a stand- alone voltage output temperature sensor. the ad596/ad597 can be powered with a single supply from +5 v to +30 v, or dual supplies up to a total span of 36 v. typical quiescent supply current is 160 m a, which minimizes self-heating errors. the ad596/ad597 h package option includes a thermocouple failure alarm that indicates an open thermocouple lead when operated in the temperature proportional measurement mode. the alarm output has a flexible format which can be used to drive relays, leds or ttl logic. the device is packaged in a reliability qualified, cost effective 10-pin metal can or soic and is trimmed to operate over an ambient temperature range from +25 c to +100 c. operation over an extended ambient temperature range is possible with slightly reduced accuracy. the ad596 will amplify thermo- couple signals covering the entire C200 c to +760 c tempera- ture range recommended for type j thermocouples while the ad597 can accommodate C200 c to +1250 c type k inputs. the ad596/ad597 has a calibration accuracy of 4 c at an ambient temperature of 60 c and an ambient temperature stability specification of 0.05 c/ c from +25 c to +100 c. if higher accuracy, or a lower ambient operating temperature is required, either the ad594 (j thermocouple) or ad595 (k thermocouple) should be considered. * protected by u.s. patent no. 4,029,974. product highlights 1. the ad596/ad597 provides cold junction compensation and a high gain amplifier which can be used as a setpoint comparator. 2. the input stage of the ad596/ad597 is a high quality in- strumentation amplifier that allows the thermocouple to float over most of the supply voltage range. 3. linearization not required for thermocouple temperatures close to 175 c (+100 c to +540 c for ad596). 4. cold junction compensation is optimized for ambient tem- peratures ranging from +25 c to +100 c. 5. in the stand-alone mode, the ad596/ad597 produces an output voltage that indicates its own temperature. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 world wide web site: http://www.analog.com fax: 781/326-8703 ? analog devices, inc., 1998 to-100 + C g fb v out +alm +in vC v+ a + ice point comp + ad596/ ad597 Calm Cin hys gnd + C g soic +in Cin top view (not to scale) ad597 g C + + g C + a + ice point comp hys v+ gnd v out vC fb 1 2 3 45 6 7 8
ad596/ad597Cspecifications (@ +60 8 c and v s = 10 v, type j (ad596), type k (ad597) thermocouple, unless otherwise noted) rev. b C2C model ad596ah ad597ah ad597ar min typ max min typ max min typ max units absolute maximum ratings +v s to Cv s 36 36 36 volts common-mode input voltage (Cv s C 0.15) +v s (Cv s C 0.15) +v s (Cv s C 0.15) +v s volts differential input voltage Cv s +v s Cv s +v s Cv s +v s volts alarm voltages +alm Cv s (Cv s +36) Cv s (Cv s +36) Cv s (Cv s +36) volts Calm Cv s +v s Cv s +v s Cv s +v s volts operating temperature range C55 +125 C55 +125 C40 +125 c output short circuit to common indefinite indefinite indefinite temperature measurement (specified temperature range +25 c to +100 c) calibration error 1 C4 +4 C4 +4 C4 +4 c stability vs. temperature 2 0.02 0.05 0.02 0.05 0.02 0.05 c/ c gain error C1.5 +1.5 C1.5 +1.5 C1.5 +1.5 % nominal transfer function 10 10 10 mv/ c amplifier characteristics closed loop gain 3 180.6 245.5 245.5 v/v input offset voltage c 53.21 + 235 c 41.27 C 37 c 41.27 C 37 m v input bias current 0.1 0.1 0.1 m a differential input range C10 +50 C10 +50 C10 +50 mv common-mode range (Cv s C 0.15) (+v s C 4) (+v s C 0.15) (+v s C 4) (Cv s C 0.15) (+v s C 4) volts common-mode sensitivityCrto 10 10 10 mv/v power supply sensitivityCrto 1 10 1 10 1 10 mv/v output voltage range dual supplies (Cv s + 2.5) (+v s C 2) (Cv s + 2.5) (+v s C 2) (Cv s + 2.5) (+v s C 2) volts single supply 0 (+v s C 2) 0 (+v s C 2) 0 (+v s C 2) volts usable output current 4 5 5 5ma 3 db bandwidth 15 15 15 khz alarm characteristics 5 alarm function not pinned out v ce(sat) at 2 ma 0.3 0.3 volts leakage current 6 1 6 1 m a operating voltage at C alm (+v s C 4) (+v s C 4) volts short circuit current 20 20 ma power requirements operating (+v s to Cv s ) 30 (+v s to Cv s ) 30 (+v s to Cv s ) 30 volts quiescent current +v s 160 300 160 300 160 300 m a Cv s 100 200 100 200 100 200 m a notes 1 this is a measure of the deviation from ideal with a measuring thermocouple junction of 175 c and a chip temperature of 60 c. the ideal transfer function is given by: ad596: v out = 180.57 (v m C v a + (ambient in c) 53.21 m v/ c + 235 m v) ad597: v out = 245.46 (v m C v a + (ambient in c) 41.27 m v/ c C 37 m v) where v m , and v a represent the measuring and ambient temperatures and are taken from the appropriate j or k thermocouple table. the ideal trans fer function minimizes the error over the ambient temperature range of 25 c to 100 c with a thermocouple temperature of approximately 175 c. 2 defined as the slope of the line connecting the ad596/ad597 cjc errors measured at 25 c and 100 c ambient temperature. 3 pin 6 shorted to pin 7. 4 current sink capability in single supply configuration is limited to current drawn to ground through a 50 k w resistor at output voltages below 2.5 v. 5 alarm function available on h package option only. specifications subject to change without notice. specifications shown in boldface are tested on all production units at final electrical test. results from those tests are used to calculate outgoing quality le vels. all min and max specifications are guaranteed, although only those shown in boldface are tested on all production units. ordering guide model package description package options ad596ah to-100 h-10a ad597ah to-100 h-10a ad597ar* plastic soic so-8 *consult factory for availability.
ad596/ad597 rev. b C3C table i. output voltage vs. thermocouple temperature (ambient +60 8 c, v s = C5 v, +15 v) thermocouple type j ad596 type k ad597 temperature voltage output voltage output 8 c mvmvmvmv C200 C7.890 C1370 C5.891 C1446 C180 C7.402 C1282 C5.550 C1362 C160 C6.821 C1177 C5.141 C1262 C140 C6.159 C1058 C4.669 C1146 C120 C5.426 C925 C4.138 C1016 C100 C4.632 C782 C3.553 C872 C80 C3.785 C629 C2.920 C717 C60 C2.892 C468 C2.243 C551 C40 C1.960 C299 C1.527 C375 C20 C.995 C125 C.777 C191 C10 C.501 C36 C.392 C96 005400 10 .507 146 .397 97 20 1.019 238 .798 196 25 1.277 285 1.000 245 30 1.536 332 1.203 295 40 2.058 426 1.611 395 50 2.585 521 2.022 496 60 3.115 617 2.436 598 80 4.186 810 3.266 802 100 5.268 1006 4.095 1005 120 6.359 1203 4.919 1207 140 7.457 1401 5.733 1407 160 8.560 1600 6.539 1605 180 9.667 1800 7.338 1801 200 10.777 2000 8.137 1997 220 11.887 2201 8.938 2194 240 12.998 2401 9.745 2392 260 14.108 2602 10.560 2592 280 15.217 2802 11.381 2794 300 16.325 3002 12.207 2996 320 17.432 3202 13.039 3201 340 18.537 3402 13.874 3406 360 19.640 3601 14.712 3611 380 20.743 3800 15.552 3817 400 21.846 3999 16.395 4024 420 22.949 4198 17.241 4232 440 24.054 4398 18.088 4440 460 25.161 4598 18.938 4649 480 26.272 4798 19.788 4857 thermocouple type j ad596 type k ad597 temperature voltage output voltage output 8 cmvmvmvmv 500 27.388 5000 20.640 5066 520 28.511 5203 21.493 5276 540 29.642 5407 22.346 5485 560 30.782 5613 23.198 5694 580 31.933 5821 24.050 5903 600 33.096 6031 24.902 6112 620 34.273 6243 25.751 6321 640 35.464 6458 26.599 6529 660 36.671 6676 27.445 6737 680 37.893 6897 28.288 6944 700 39.130 7120 29.128 7150 720 40.382 7346 29.965 7355 740 41.647 7575 30.799 7560 750 42.283 7689 31.214 7662 760 C C 31.629 7764 780 C C 32.455 7966 800 C C 33.277 8168 820 C C 34.095 8369 840 C C 34.909 8569 860 C C 35.718 8767 880 C C 36.524 8965 900 C C 37.325 9162 920 C C 38.122 9357 940 C C 38.915 9552 960 C C 39.703 9745 980 C C 40.488 9938 1000 C C 41.269 10130 1020 C C 42.045 10320 1040 C C 42.817 10510 1060 C C 43.585 10698 1080 C C 44.439 10908 1100 C C 45.108 11072 1120 C C 45.863 11258 1140 C C 46.612 11441 1160 C C 47.356 11624 1180 C C 48.095 11805 1200 C C 48.828 11985 1220 C C 49.555 12164 1240 C C 50.276 12341 1250 C C 50.633 12428
ad596/ad597 rev. b C4C temperature proportional output mode the ad596/ad597 can be used to generate a temperature proportional output of 10 mv/ c when operated with j and k type thermocouples as shown in figure 1. thermocouples pro- duce low level output voltages which are a function of both the temperature being measured and the reference or cold junction temperature. the ad596/ad597 compensates for the cold junction temperature and amplifies the thermocouple signal to produce a high level 10 mv/ c voltage output which is a func- tion only of the temperature being measured. the temperature stability of the part indicates the sensitivity of the output voltage to changes in ambient or device temperatures. this is typically 0.02 c/ c over the +25 c to +100 c recommended ambient temperature range. the parts will operate over the extended ambient temperature ranges from C55 c to +125 c, but ther- mocouple nonlinearity at the reference junction will degrade the temperature stability over this extended range. table i is a list of ideal ad596/ad597 output voltages as a function of celsius temperature for type j and k ansi standard thermocouples with package and reference junction at 60 c. as is normally the case, these outputs are subject to calibration and temperature sensitivity errors. these tables are derived using the ideal trans- fer functions: ad596 output = (type j voltage + 301.5 m v) 180.57 ad597 output = (type k voltage) 245.46 0.01 m f 1m v +15v C15v 100k v 10k v 100k v constantan (alumel) iron (chromel) optional offset adjust 0.01 m f v out +5v to +30v 0 to C25v span of +5v to +30v ad596/ ad597* *h package pinout shown figure 1. temperature proportional output connection the offsets and gains of these devices have been laser trimmed to closely approximate thermocouple characteristics over mea- surement temperature ranges centered around 175 c with the ad596/ad597 at an ambient temperature between 25 c and 100 c. this eliminates the need for additional gain or offset adjustments to make the output voltage read: v out = 10 mv/ c (thermocouple temperature in c) (within specified tolerances). excluding calibration errors, the above transfer function is accu- rate to within 1 c from +80 c to +550 c for the ad596 and C20 c to +350 c for the ad597. the different temperature ranges are due to the differences in j and k type thermocouple curves. european din fe-cuni thermocouple vary slightly from ansi type j thermocouples. table i does not apply when these types of thermocouples are used. the transfer functions given previ- ously and a thermocouple table should be used instead. figure 1 also shows an optional trimming network which can be used to change the devices offset voltage. injecting or sinking 200 na from pin 3 will offset the output approximately 10 mv (1 c). the ad596/ad597 can operate from a single supply from 5 v to 36 v or from split supplies totalling 36 v or less as shown. since the output can only swing to within 2 v of the positive supply, the usable measurement temperature range will be re- stricted when positive supplies less than 15 v for the ad597 and 10 v for the ad596 are used. if the ad596/ad597 is to be used to indicate negative celsius temperatures, then a negative supply is required. common-mode voltages on the thermocouple inputs must remain within the common-mode voltage range of the ad596/ ad597, with a return path provided for the bias currents. if the thermocouple is not remotely grounded, then the dotted line connection shown in figure 1 must be made to one of the ther- mocouple inputs. if there is no return path for the bias currents, the input stage will saturate, causing erroneous output voltages. in this configuration, the ad596/ad597 h package option has circuitry which detects the presence of an open thermocouple. if the thermocouple loop becomes open, one or both of the inputs to the device will be deprived of bias current causing the output to saturate. it is this saturation which is detected internally and used to activate the alarm circuitry. the output of this feature has a flexible format which can be used to source or sink up to 20 ma of current. the collector (+alm) should not be allowed to become more positive than (Cv s + 36 v), however, it may be permitted to be more positive than +v s . the emitter voltage (Calm) should be constrained such that it does not become more positive than 4 v below +v s . if the alarm feature is not used, this pin should be connected to pins 4 or 5 as shown in figure 1. the alarm function is unavailable on the ar package option.
ad596/ad597 rev. b C5C setpoint control mode the ad596/ad597 can be connected as a setpoint controller as shown in figure 2. the thermocouple voltage is cold junction compensated, amplified, and compared to an external setpoint voltage. the relationship between setpoint voltage and tempera- ture is given in table i. if the temperature to be controlled is within the operating range (C55 c to +125 c) of the device, it can monitor its own temperature by shorting the inputs to ground. the setpoint voltage with the thermocouple inputs grounded is given by the expressions: ad596 setpoint voltage = c 9.6 mv/ c + 42 mv ad597 setpoint voltage = c 10.1 mv/ c C 9.1 mv the input impedance of the setpoint pin of the ad596/ad597 is approximately 50 k w . the temperature coefficient of this resistance is 15 ppm/ c. therefore, the 100 ppm/ c 5 k w pot shown in figure 2 will only introduce an additional 1 c degra- dation of temperature stability over the +25 c to +100 c ambi- ent temperature range. ad596/ ad597* constantan (alumel) iron (chromel) 0.01 m f +v r hysteresis (optional) temperature controlled region heater driver temperature comparator output set- point voltage v ref 5k v 100ppm/ 8 c set- point voltage *h package pinout shown figure 2. setpoint control mode switching hysteresis is often used in setpoint systems of this type to provide noise immunity and increase system reliability. by reducing the frequency of on-off cycling, mechanical component wear is reduced leading to enhanced system reliability. this can easily be implemented with a single external resistor between pins 7 and 3 of the ad596/ad597. each 200 na of current injected into pin 3 when the output switches will cause about 1 c of hysteresis; that is: r hyst ( w ) = v out 200 na 1 c hyst in the setpoint configuration, the ad596/ad597 output is saturated at all times, so the alarm transistor will be on regard- less of whether there is an open circuit or not. however, Calm must be tied to a voltage below (+v s C 4 v) for proper operation of the rest of the circuit. stand-alone temperature transducer the ad596/ad597 may be configured as a stand-alone celsius thermometer as shown in figure 3. 0.01 m f Cv s v out 9.6mv/ 8 c +v s 0.01 m f + C g a + ice point comp + ad596/ ad597* + C g *h package pinout shown figure 3. stand-alone temperature transducer temperature proportional output connection simply omit the thermocouple and connect the inputs (pins 1 and 2) to common. the output will now reflect the compensa- tion voltage and hence will indicate the ad596/ad597 tem- perature. in this three terminal, voltage output, temperature sensing mode, the ad596/ad597 will operate over the full extended C55 c to +125 c temperature range. the output scaling will be 9.6 mv per c with the ad596 and 10.1 mv per c with the ad597. additionally there will be a 42 mv offset with the ad596 causing it to read slightly high when used in this mode. thermocouple connections the connection of the thermocouple wire and the normal wire or printed circuit board traces going to the ad596/ad597 forms an effective reference junction as shown in figure 4. this junction must be kept at the same temperature as the ad596/ ad597 for the internal cold junction compensation to work properly. unless the ad596/ad597 is in a thermally stable enclosure, the thermocouple leads should be brought in directly to pins 1 and 2. reference junction constantan (alumel) iron (chromel) note: a bias return path from pins 1 and 2 of less than 1k v impedance must be provided. 0.01 m f ad596/ ad597* limiting resistor to led 0.01 m f +v s v out *h package pinout shown gnd Cv s figure 4. pcb connections to ensure secure bonding, the thermocouple wire should be cleaned to remove oxidization prior to soldering. noncorrosive resin flux is effective with iron, constantan, chromel, and alumel, and the following solders: 95% tinC5% silver, or 90% tinC10% lead.
ad596/ad597 rev. b C6C single and dual supply connections in the single supply configuration as used in the setpoint con- troller of figure 2, any convenient voltage from +5 v to +36 v may be used, with self-heating errors being minimized at lower supply levels. in this configuration, the Cv s connection at pin 5 is tied to ground. temperatures below zero can be accommo- dated in the single supply setpoint mode, but not in the single supply temperature measuring mode (figure 1 reconnected for single supply). temperatures below zero can only be indicated by a negative output voltage, which is impossible in the single supply mode. common-mode voltages on the thermocouple inputs must remain below the positive supply, and not more than 0.15 v more negative than the minus supply. in addition, a return path for the input bias currents must be provided. if the thermo- couple is not remotely grounded, then the dotted line connec- tions in figures 1 and 2 are mandatory. stability over temperature the ad596/ad597 is specified for a maximum error of 4 c at an ambient temperature of 60 c and a measuring junction temperature at 175 c. the ambient temperature stability is specified to be a maximum of 0.05 c/ c. in other words, for every degree change in the ambient temperature, the output will change no more than 0.05 degrees. so, at 25 c the maximum deviation from the temperature-voltage characteristic of table i is 5.75 c, and at 100 c it is 6 c maximum (see figure 5). if the offset error of 4 c is removed with a single offset adjust- ment, these errors will be reduced to 1.75 c and 2 c max. the optional trim circuit shown in figure 1 demonstrates how the ambient offset error can be adjusted to zero. maximum maximum typical 25 8 c 100 8 c 60 8 c +2.0 8 c +1.75 8 c +0.8 8 c 0 C0.8 8 c C1.75 8 c C2.0 8 c figure 5. drift error vs. temperature thermal environmental effects the inherent low power dissipation of the ad596/ad597 keeps self-heating errors to a minimum. however, device output is capable of delivering 5 ma to an external load and the alarm circuitry can supply up to 20 ma. since the typical junction to ambient thermal resistance in free air is 150 c/w, significant temperature difference between the package pins (where the reference junction is located) and the chip (where the cold junc- tion temperature is measured and then compensated) can exist when the device is operated in a high dissipation mode. these temperature differences will result in a direct error at the out- put. in the temperature proportional mode, the alarm feature will only activate in the event of an open thermocouple or sys- tem transient which causes the device output to saturate. self-heating errors will not effect the operation of the alarm but two cases do need to be considered. first, after a fault is cor- rected and the alarm is reset, the ad596/ad597 must be al- lowed to cool before readings can again be accurate. this can take 5 minutes or more depending upon the thermal environ- ment seen by the device. second, the junction temperature of the part should not be allowed to exceed 150 c. if the alarm circuit of the ad596/ad597 is made to source or sink 20 ma with 30 v across it, the junction temperature will be 90 c above ambient causing the die temperature to exceed 150 c when ambient is above 60 c. in this case, either the load must be reduced, or a heat sink used to lower the thermal resistance. temperature readout and control figure 6 shows a complete temperature indication and control system based on the ad596/ad597. here the ad596/ad597 is being used as a closed-loop thermocouple signal conditioner and an external op amp is used to implement setpoint. this has two important advantages. it provides a high level (10 mv/ c) output for the a/d panel meter and also preserves the alarm function for open thermocouples. the a/d panel meter can easily be offset and scaled as shown to read directly in degrees fahrenheit. if a two temperature cali- bration scheme is used, the dominant residual errors will arise from two sources; the ambient temperature rejection (typically 2 c over a 25 c to 100 c range) and thermocouple nonlin- earity typical +1 c from 80 c to 550 c for type j and +1 c from C20 c to 350 c for type k. an external voltage reference is used both to increase the stabil- ity of the a/d converter and supply a stable reference for the setpoint voltage. a traditional requirement for the design of setpoint control thermocouple systems has been to configure the system such that the appropriate action is taken in the event of an open thermocouple. the open thermocouple alarm pin with its flex- ible current-limited output format supports this function when the part operates in the temperature proportional mode. in addition, if the thermocouple is not remotely grounded, it is possible to program the device for either a positive or negative full-scale output in the event of an open thermocouple. this is done by connecting the bias return resistor directly to pin 1 if a high output voltage is desired to indicate a fault condition. al- ternately, if the bias return is provided on the thermocouple lead connected to pin 2, an open circuit will result in an output low reading. figure 6 shows the ground return connected to pin 1 so that if the thermocouple fails, the heater will remain off. at the same time, the alarm circuit lights the led signalling the need to service the thermocouple. grounding pin 2 would lead to low output voltage saturation, and in this circuit would result in a poten tially dangerous thermal runaway under fault conditions.
ad596/ad597 rev. b C7C ad596/ ad597* constantan (alumel) iron (chromel) +v temperature heater +v op07 + C 120v ac 1k v 10m v 10k v set-point adjust 5k v ad584 +v 10k v 10k v in hi in lo ref hi ref lo icl7136 40.2k v 1.27m v 45.2k v lcd display readout 8 f 470 v 5v + C *h package pinout shown figure 6. temperature measurement and control
ad596/ad597 rev. b C8C printed in u.s.a. c831bC5C2/98 outline dimensions dimensions shown in inches and (mm). 10-pin metal can (to-100) 0.250 (6.35) min 0.750 (19.05) 0.500 (12.70) 0.185 (4.70) 0.165 (4.19) reference plane 0.050 (1.27) max 0.019 (0.48) 0.016 (0.41) 0.021 (0.53) 0.016 (0.41) 0.045 (1.14) 0.010 (0.25) 0.040 (1.02) max base & seating plane 0.335 (8.51) 0.305 (7.75) 0.370 (9.40) 0.335 (8.51) 1 0.034 (0.86) 0.027 (0.69) 0.045 (1.14) 0.027 (0.69) 0.160 (4.06) 0.110 (2.79)
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