Pt100 and Pt1000 are among the most commonly used platinum resistance sensors for industrial temperature measurement. They are used in machines, heating and air-conditioning systems, process vessels, pipelines, test benches, laboratory equipment, control cabinets and many other applications.
At first glance, the two sensors appear to differ only by an additional zero in their designation. In practice, however, the different nominal resistance has a significant effect on lead resistance, measuring current, electronics and interchangeability. A Pt100 has a resistance of 100 Ω at 0 °C, while a Pt1000 has a resistance of 1,000 Ω.
For the same temperature change, the Pt1000 provides an approximately ten times greater change in resistance. This is particularly advantageous with a two-wire connection and in compact electronic measuring systems. With a correctly implemented three- or four-wire measurement, however, the lead resistance is largely or almost completely compensated. The advantage of the Pt1000 then becomes considerably smaller.
A Pt1000 is also not automatically more accurate than a Pt100. Both can comply with the same tolerance class according to IEC 60751. The actual measuring accuracy additionally depends on the sensor construction, installation situation, measuring current, connection cable and evaluation electronics.
This article explains the difference between Pt100 and Pt1000, compares the different wiring configurations and shows when a Pt100, a Pt1000 or a temperature transmitter is the most suitable solution.
Table of contents
- How a platinum resistance thermometer works
- The fundamental difference between Pt100 and Pt1000
- Resistance characteristic and sensitivity
- Is a Pt1000 more accurate than a Pt100?
- Why lead resistance influences the measured value
- Pt100 and Pt1000 in a two-wire connection
- Three-wire connection as the industrial standard
- Four-wire connection for particularly accurate measurements
- Comparison of 2-, 3- and 4-wire connections
- Considering measuring current and self-heating
- Thin-film and wire-wound sensing elements
- Does Pt100 or Pt1000 influence the response time?
- Temperature range and tolerance class
- Compatibility with PLCs, displays and controllers
- When a temperature transmitter is useful
- Are Pt100 and Pt1000 interchangeable?
- Typical applications for Pt100 and Pt1000
- Practical selection guide
- Typical incorrect orders and wiring errors
- Practical example: Temperature deviation caused by a long two-wire cable
- Testing the sensor and evaluation electronics
- Which measuring instruments / products are suitable?
- Conclusion
- Frequently asked questions about Pt100 and Pt1000
How a platinum resistance thermometer works
A resistance thermometer uses the property of metals to change their electrical resistance with temperature. With platinum, the resistance increases as the temperature rises. It is therefore a sensor with a positive temperature coefficient.
The evaluation electronics pass a small measuring current through the sensing element and measure the resulting voltage drop. The electrical resistance is determined from the voltage and current. The instrument then calculates the temperature using the standardised resistance-temperature characteristic.
Platinum is particularly suitable for precise temperature measurements because its characteristic is reproducible, stable over the long term and internationally standardised. The requirements for industrial platinum resistance sensors and complete resistance thermometers are described in IEC 60751.
The designation begins with “Pt” for platinum. The number that follows indicates the nominal resistance of the sensor at 0 °C. A Pt100 has a nominal resistance of 100 Ω at 0 °C, while a Pt1000 has a nominal resistance of 1,000 Ω.
The sensor may be designed as an individual sensing element, cable temperature sensor, threaded sensor, measuring insert or complete resistance thermometer with a connection head and thermowell. The actual measuring resistor is therefore only one component of the complete temperature measuring point.
The fundamental difference between Pt100 and Pt1000
Pt100 and Pt1000 fundamentally use the same standardised platinum characteristic. The relative temperature coefficient is the same. However, the Pt1000 has approximately ten times the resistance of the Pt100 across the entire temperature range.
| Characteristic | Pt100 | Pt1000 |
|---|---|---|
| Nominal resistance at 0 °C | 100 Ω | 1,000 Ω |
| Resistance at 100 °C | approx. 138.5 Ω | approx. 1,385 Ω |
| Average resistance change between 0 and 100 °C | approx. 0.385 Ω/K | approx. 3.85 Ω/K |
| Influence of the same lead resistance | comparatively high | approximately ten times lower |
| Availability in industrial installations | very widespread | frequently used in compact and electronic applications |
| Required electronics input | Pt100-compatible | Pt1000-compatible |
The tenfold resistance is the most important practical advantage of the Pt1000. An additional lead resistance of 1 Ω, for example, represents a considerably larger proportion of the sensor signal with a Pt100 than with a Pt1000.
However, with a correctly compensated three- or four-wire connection, this advantage becomes less important. In such applications, a Pt100 may be the more practical solution due to its widespread use, the large selection of available instruments and its compatibility with existing industrial components.
Resistance characteristic and sensitivity
Between 0 and 100 °C, the nominal resistance of a Pt100 rises from 100 Ω to approximately 138.5 Ω. Over the same temperature range, a Pt1000 rises from 1,000 Ω to approximately 1,385 Ω.
The absolute resistance change per kelvin is therefore approximately ten times greater with the Pt1000. The evaluation electronics can consequently detect a small temperature change as a larger change in resistance.
This greater electrical sensitivity is particularly advantageous when the electronics are optimised for Pt1000 and lead resistances cannot be compensated by a three- or four-wire connection.
However, a larger resistance change does not automatically mean ten times better temperature accuracy. The measuring accuracy remains limited by the tolerance class of the sensor, the resolution and accuracy of the electronics, the measuring current, self-heating and the installation situation.
The characteristic is also not completely linear across the entire temperature range. The evaluation unit must therefore use the standardised characteristic function or a corresponding table. A simple linear conversion may cause additional deviations over wide temperature ranges.
Is a Pt1000 more accurate than a Pt100?
A Pt1000 is not fundamentally more accurate than a Pt100. If both sensors have the same tolerance class and are operated with suitable electronics in the same installation situation, generally comparable permissible temperature deviations apply.
The tolerance class describes the deviation of the sensing element from the standardised characteristic. Frequently used classes include B, A and AA. The permissible deviation increases with temperature and also depends on the permissible operating range of the particular sensor version.
Additional error components must be considered for the complete measuring point:
- tolerance of the sensing element
- lead resistance and wiring configuration
- accuracy of the evaluation electronics
- measuring current and self-heating
- heat conduction through the sensor and process connection
- immersion depth and thermal contact
- ageing, drift and mechanical loading
- temperature differences within the measuring point
A Pt1000 can have a significantly smaller lead error in a two-wire connection. However, this practical advantage must not be confused with a tighter sensor tolerance.
A Pt100 in a four-wire connection can provide a considerably better overall measurement than a Pt1000 in a two-wire connection when high accuracy is required.
Why lead resistance influences the measured value
The connection cable between the sensor and evaluation instrument has its own electrical resistance. This depends on the cable length, conductor cross-section, conductor material and cable temperature.
In a simple two-wire measurement, the resistance of both connecting conductors is connected in series with the sensing element. The evaluation electronics cannot distinguish which proportion originates from the sensor and which from the cable.
Because the resistance of a platinum sensor increases as the temperature rises, additional lead resistance is interpreted as an excessively high temperature.
For small ranges, the approximate temperature error can be calculated in simplified form from the total lead resistance and the resistance change of the sensor:
Temperature error ≈ lead resistance / resistance change per kelvin
If the outgoing and return conductors together cause an additional resistance of 1 Ω, for example, the resulting error is approximately 2.6 K with a Pt100. With a Pt1000, the error is only approximately 0.26 K.
This example calculation applies approximately in the range around 0 °C. The exact slope of the characteristic changes slightly with temperature.
Pt100 and Pt1000 in a two-wire connection
The two-wire connection is the simplest connection method. Two conductors connect the measuring resistor to the evaluation electronics. The resistance of both conductors is included completely in the measured result.
With short cables, large conductor cross-sections and moderate accuracy requirements, a two-wire connection may be sufficient. It is particularly simple, requires few terminals and can be implemented with inexpensive cables.
The Pt1000 offers a clear advantage in this case. Because its resistance signal is approximately ten times greater, the same absolute lead resistance causes only around one tenth of the temperature error of a Pt100.
Nevertheless, the influence of the cable must not be ignored completely even with a Pt1000. A relevant deviation can still occur with long, thin or hot cables. The copper resistance of the cable also changes with ambient temperature.
A fixed correction of the lead resistance in the electronics can only work reliably if the cable length, cross-section and cable temperature remain sufficiently constant.
For high accuracy requirements, a three- or four-wire connection is generally more suitable than a mathematically corrected two-wire measurement.
Three-wire connection as the industrial standard
The three-wire connection uses three connecting conductors. Two conductors are connected to one side of the measuring resistor, while the third is connected to the opposite side.
The evaluation electronics use the additional information to compensate for the lead resistance to a large extent. This requires the resistances of the relevant connecting conductors to be as equal as possible.
Different cable lengths, cross-sections, terminal connections or temperatures can cause an imbalance. This difference is not compensated completely and remains as a residual error.
In industrial installations, the three-wire connection often provides a good compromise between accuracy, wiring effort and cost. It is therefore very widely used with Pt100 resistance thermometers.
A Pt1000 can also be operated in a three-wire connection, provided that the sensor and evaluation electronics are designed for it. Combined with the inherently smaller relative influence of the lead resistance, this can provide a very robust measurement.
The three conductors should originate from the same cable, have the same cross-section and be routed along the same cable path. Individually extended conductors can reduce the effectiveness of the compensation.
Four-wire connection for particularly accurate measurements
With the four-wire connection, two conductors are used to supply the measuring current and two separate conductors are used to measure the voltage. As practically no relevant current flows through the voltage measurement conductors, their lead resistances cause virtually no voltage drop.
The resistance of the sensing element can therefore be determined independently of the resistance of the connecting cables. Unequal conductor resistances are also largely eliminated.
The four-wire connection is particularly suitable for laboratory and calibration technology, reference measurements, long cables and applications with very small permissible measurement uncertainties.
The additional wiring effort is greater. The sensor, connector, terminals and evaluation electronics must also support a genuine four-wire connection.
With a four-wire measurement, there is little difference between Pt100 and Pt1000 in terms of lead error. The decision can then be based more strongly on electronics compatibility, sensor design, availability and measuring current.
Comparison of 2-, 3- and 4-wire connections
| Connection method | Influence of the cable | Advantages | Typical application |
|---|---|---|---|
| 2-wire | included completely in the measured value | low wiring effort | short cables, Pt1000, simple HVAC and machine applications |
| 3-wire | largely compensated, residual error in the event of imbalance | good compromise between accuracy and effort | industrial Pt100 and Pt1000 measuring points |
| 4-wire | almost completely eliminated | highest accuracy even with long cables | laboratories, calibration and precision measurement |
The number of available conductors alone does not confirm the measuring configuration that is being used. A four-wire sensor can also be connected as a three- or two-wire sensor by combining or omitting individual conductors. However, some of the benefits of the original connection are then lost.
The data sheet, wiring diagram and terminal assignment should therefore be checked before connection. Particularly with dual sensors, additional conductors may be provided for a second Pt100 or Pt1000 element.
Considering measuring current and self-heating
To measure resistance, the evaluation electronics must pass an electrical measuring current through the sensing element. This current generates power loss and therefore heat in the resistor.
The electrical power is calculated as follows:
P = I² × R
If the same measuring current were used for a Pt1000 as for a Pt100, approximately ten times the power loss would occur due to the tenfold resistance. Suitable Pt1000 inputs therefore often operate with a correspondingly smaller measuring current.
The actual temperature increase does not depend solely on the electrical power. How effectively the sensor can dissipate heat to the medium or component is also decisive.
Self-heating is generally considerably lower in moving water than in still air or in an installation with poor thermal conductivity. Small sensing elements are particularly sensitive to an excessively high measuring current.
A Pt1000 must therefore not simply be connected to any resistance measurement input. The electronics must use a suitable measuring current and must be designed for the Pt1000 characteristic.
Thin-film and wire-wound sensing elements
In addition to the choice between Pt100 and Pt1000, the construction of the platinum measuring resistor must also be considered. Thin-film and wire-wound sensing elements are commonly used.
With a thin-film sensor, a very thin platinum layer is applied to a ceramic substrate. These elements are compact, resistant to vibration and economical to manufacture.
Wire-wound sensors use a very fine platinum wire. Depending on their design, they may be suitable for wider temperature ranges or special accuracy requirements, but they require more space and can be more sensitive to severe vibration.
Pt100 sensing elements are available in numerous thin-film and wire-wound versions. Pt1000 elements are frequently used as compact thin-film designs.
Product selection must therefore not be based solely on the nominal resistance and tolerance class. The temperature range, vibration loading, dimensions and long-term stability of the specific sensing element must also be suitable.
Does Pt100 or Pt1000 influence the response time?
The nominal resistance alone does not determine the thermal response time. A Pt100 and a Pt1000 with identical dimensions, the same sensor housing and the same installation situation can have very similar response behaviour.
The decisive factors are primarily:
- dimensions and mass of the sensing element
- diameter and wall thickness of the protective tube
- thermal contact between the element and sensor tip
- medium and flow velocity
- immersion depth
- additional thermowell or protective tube
- air gaps and heat-conducting materials
A small Pt1000 thin-film sensor can respond very quickly. However, a Pt100 in a comparable design can respond just as quickly. Conversely, a Pt1000 also responds slowly if it is installed in a solid thermowell with a large air gap.
For fast processes, a specific t50 or t90 value under defined test conditions should therefore be requested. The Pt100 or Pt1000 designation alone does not permit a reliable conclusion regarding the response time.
Temperature range and tolerance class
The theoretical and standardised characteristic range of a platinum resistance sensor is not automatically the same as the permissible temperature range of a complete sensor assembly.
The usable range is limited by factors including the sensing element, protective tube, connection cable, transition sleeve, process connection and tolerance class.
A cable resistance thermometer, for example, may contain a sensing element that can withstand high temperatures, while the attached PVC, silicone or PTFE cable is only designed for a considerably lower temperature range.
The tolerance class may also only apply within a defined temperature range. A sensor may continue to function outside this range without still meeting the originally ordered class there.
For a technically correct enquiry, both the normal operating range and any possible start-up, cleaning and fault temperatures should therefore be specified.
Compatibility with PLCs, displays and controllers
Pt100 and Pt1000 cannot be used with the same evaluation electronics without adjustment. An input must support the correct characteristic, suitable measuring range and intended connection method.
If a Pt1000 is connected to an input designed exclusively for Pt100, the instrument interprets the considerably higher resistance incorrectly. Depending on the measuring range, it may display an extremely high temperature, a sensor fault or a measuring-range overflow.
Conversely, if a Pt100 is connected to a Pt1000 input, the resistance is far below the expected range. The display may indicate a very low temperature or report a short circuit.
The following specifications must therefore be checked before replacing a sensor:
- supported sensor type: Pt100 or Pt1000
- 2-, 3- or 4-wire input
- measuring range and tolerance class
- permissible lead resistance
- measuring current and sensor-break detection
- number of sensors per probe
- terminal assignment and shielding
Many modern universal transmitters and temperature measuring instruments can be switched between Pt100 and Pt1000. However, this function must be stated explicitly in the instrument documentation.
When a temperature transmitter is useful
With long cable runs, a temperature transmitter can be installed directly in the connection head, inside the sensor housing or close to the sensor. It measures the Pt100 or Pt1000 resistance locally and converts it, for example, into a 4–20 mA signal.
This keeps the sensitive resistance connection between the sensor and transmitter short. Further transmission through the current loop is considerably less sensitive to lead resistance and electromagnetic interference.
A transmitter is particularly useful for:
- long cables to the PLC or control system
- severe electromagnetic interference
- standardised 4–20 mA inputs
- galvanic isolation between the sensor and evaluation system
- configurable measuring ranges
- required sensor-break and short-circuit diagnostics
The transmitter must be suitable for the sensor type and connection method. An instrument that supports Pt100 and Pt1000 must be configured for the sensor that is actually connected before commissioning.
For electrical testing of a 4–20 mA current loop, the UPS4E loop calibrator can be used as a supplementary instrument. It can measure the loop current or simulate defined current values to test the PLC input.
However, the UPS4E does not directly test the resistance of a Pt100 or Pt1000 sensor. A suitable resistance or temperature simulator is required to test the RTD input.
Are Pt100 and Pt1000 interchangeable?
Pt100 and Pt1000 are often available in similar sensor housings mechanically, but they are not directly interchangeable electrically.
Replacement is only possible if the evaluation electronics can be changed to the new sensor type. The connection method, terminal assignment, measuring range, sensor current and diagnostic functions must also be compatible.
Even with an identical design, the following characteristics may differ:
- response time
- permissible temperature range
- tolerance class
- thin-film or wire-wound construction
- single or dual sensor
- number of conductors
- sensor length and diameter
- process connection
Ordering a Pt1000 as a supposedly “more accurate replacement” for a Pt100 can therefore result in a non-functional measuring point.
Before ordering a replacement, the complete type designation, wiring diagram, number and colour of the connecting conductors and the parameter settings of the evaluation instrument should be checked.
Typical applications for Pt100 and Pt1000
Pt100 sensors are very widely used in conventional industrial and process applications. Many temperature transmitters, PLC modules, controllers and handheld measuring instruments are designed for Pt100 as standard.
Typical applications include process vessels, pipelines, bearings, motors, machines, test benches and calibration tasks. Three- or four-wire connections are frequently used with longer cables.
Pt1000 sensors are particularly useful when a simple two-wire connection is intended and the influence of the cable should remain small. They are used, among other applications, in building automation, heating, ventilation and air-conditioning systems, as well as in compact electronic instruments.
The areas of application overlap considerably. A Pt1000 is not limited to building automation, and a Pt100 can of course also be used in a simple two-wire connection.
The decision should always be based on the available electronics, cable length, accuracy target and mechanical design of the sensor.
Practical selection guide
| Requirement | Generally suitable solution | Reason |
|---|---|---|
| Existing industrial installation with Pt100 input | Pt100 | Direct compatibility and large selection of instruments |
| Short two-wire cable and moderate accuracy | Pt100 or Pt1000 | Either may be suitable depending on the cable and electronics |
| Longer two-wire cable without compensation capability | Pt1000 | Lower relative influence of the lead resistance |
| Standard industrial measuring point with a longer cable | Pt100 in 3-wire or Pt1000 in 3-wire | Influence of the cable is largely compensated |
| Precision or calibration measurement | Pt100 or Pt1000 in 4-wire | Lead resistance is almost completely eliminated |
| Very long cable run to the PLC | RTD with a local 4–20 mA transmitter | Robust signal transmission and diagnostic capabilities |
| Evaluation instrument supports Pt100 only | Pt100 | Pt1000 would not be electrically compatible |
| Compact electronics with an expressly specified Pt1000 input | Pt1000 | High resistance and large absolute signal change |
This guidance does not replace an assessment of the specific measuring point. A chemically unsuitable thermowell material or insufficient immersion depth can cause a greater measuring error than the decision between Pt100 and Pt1000.
Typical incorrect orders and wiring errors
| Error | Possible consequence | Better approach |
|---|---|---|
| Pt1000 connected to a Pt100 input | Excessively high temperature, measuring-range overflow or sensor fault | Check the sensor type and input configuration |
| Pt100 connected to a Pt1000 input | Low-temperature or short-circuit indication | Use a suitable sensor or reconfigure the input |
| Pt100 with a long two-wire cable | Constant positive temperature error | Consider a 3-/4-wire connection, Pt1000 or transmitter |
| Unequal conductors in a three-wire connection | Incomplete lead compensation | Use equal lengths, cross-sections and cable routing |
| Four-wire sensor bridged incorrectly | Measuring error or no signal | Observe the wiring diagram of the sensor and input |
| Pt1000 ordered generally as the more accurate option | No improvement or lack of compatibility | Assess the complete measuring chain and tolerance class |
| Measuring current too high | Self-heating of the sensing element | Use a suitable RTD input |
| Sensor installed too shallowly | Heat conduction error despite correct resistance | Check immersion depth and thermal contact |
| Only the sensor class considered | Overall measuring deviation underestimated | Include the cable, electronics and installation in the measurement uncertainty |
Practical example: Temperature deviation caused by a long two-wire cable
In a heating system, the water temperature is measured using a Pt100 in a two-wire connection. The sensor is located approximately 20 m from the control cabinet.
The temperature indication is continuously around 2 °C higher than an independent reference thermometer. The sensor is initially replaced with a new Pt100, without any significant change in the deviation.
During further testing, the resistance of the connection cable is examined. The outgoing and return conductors together generate an additional resistance that the Pt100 input interprets completely as part of the sensor signal.
As the deviation is similar with both Pt100 sensors, there is no random sensor defect. The cause is the systematic lead error of the two-wire connection.
One possible solution would be to replace the sensor with a Pt1000. With the same lead resistance, the temperature error would be reduced to approximately one tenth. However, the existing controller only supports Pt100 and cannot be reconfigured.
The cable is therefore converted to a three-wire connection and a suitable Pt100 three-wire sensor is installed. Once connected correctly, the controller largely compensates for the symmetrical lead resistance.
With an even longer cable or severe electromagnetic interference, a temperature transmitter installed directly at the measuring point would be a suitable alternative. It could measure the Pt100 value locally and transmit it to the control cabinet as a 4–20 mA signal.
The example shows that a Pt1000 can reduce a lead error, but is not automatically the best or simplest solution. Compatibility with the existing electronics is also decisive.
Testing the sensor and evaluation electronics
For an initial plausibility check, the sensor can be disconnected electrically from the evaluation instrument and checked using a suitable resistance measuring instrument.
At approximately 0 °C, a Pt100 should have a resistance of about 100 Ω and a Pt1000 about 1,000 Ω. At room temperature, the values are correspondingly higher.
However, a simple resistance measurement does not yet confirm the accuracy of the sensor. Contact resistances, measuring current and measuring instrument tolerance can influence the result.
A suitable Pt100 or Pt1000 simulator can be used to test the input of a PLC, controller or transmitter. It generates defined resistance values corresponding to specific temperatures.
If the indication is correct with simulated resistance values, the cause of a deviation is probably located in the sensor, connection cable or installation situation. If the electronics already display incorrect values with the simulator, the parameter settings, input, wiring and scaling must be checked.
For a complete temperature calibration, the sensor must be compared with a traceable reference thermometer in a suitable calibration bath or dry-block calibrator. Both sensors must actually measure the same temperature.
Which measuring instruments / products are suitable?
The temperature sensors and temperature probes category contains different solutions for industry, mechanical engineering, building automation, laboratory and process applications.
The category includes resistance thermometers, thermocouples, cable and threaded sensors, surface and air sensors, as well as versions with thermowells, connection heads or integrated transmitters.
The resistance thermometers and Pt100 sensors category includes different Pt100 and Pt1000 versions with 2-, 3- or 4-wire connections. Depending on the model, compact threaded sensors, mineral-insulated cable versions, process resistance thermometers and explosion-protected versions are available.
At least the following information is required for selection:
- Pt100 or Pt1000
- 2-, 3- or 4-wire connection
- required tolerance class
- minimum and maximum temperature range
- sensor diameter and insertion length
- process connection and thermowell
- medium, pressure and flow
- connection cable and cable length
- vibration and ambient conditions
- existing PLC, controller or transmitter input
- calibration and approval requirements
The APAQ R130RTD temperature transmitter supports Pt100 and Pt1000 inputs in three- or four-wire configurations and converts the temperature value into a 4–20 mA signal. It is particularly suitable for longer cable runs to a PLC and for standardised industrial current loops.
For mobile or temporary measurements, the C.A 1823 temperature measuring instrument can be used with compatible Pt100 and Pt1000 sensors. In addition to displaying the temperature, it enables temperature profiles to be recorded and evaluated later.
For 4–20 mA temperature transmitters, the UPS4E loop calibrator is suitable as a supplementary instrument for electrical commissioning and troubleshooting. It tests the current loop, but does not replace a Pt100 or Pt1000 simulator.
ICS Schneider Messtechnik assists with selection based on the existing evaluation electronics, cable length, accuracy requirements and mechanical measuring point. Particularly for replacement sensors, the complete type designation of the existing sensor and connected instrument should be provided.
Conclusion: Pt1000 reduces the influence of lead resistance, while Pt100 offers maximum industrial compatibility
Pt100 and Pt1000 use the same standardised platinum characteristic. The essential difference is the nominal resistance at 0 °C: 100 Ω for the Pt100 and 1,000 Ω for the Pt1000.
Due to its tenfold higher resistance, the same lead resistance causes approximately only one tenth of the temperature error with a Pt1000 in a two-wire connection. This makes the Pt1000 particularly useful for simple two-wire applications and compatible compact electronics.
With a three- or four-wire connection, the influence of the cable is largely or almost completely compensated. The advantage of the Pt1000 then becomes smaller. In many industrial applications, the Pt100 offers the advantage of widespread use and a large selection of compatible transmitters, controllers and PLC modules.
A Pt1000 is not fundamentally more accurate. Both sensor types can have the same tolerance class. For the actual accuracy, the sensor construction, cable, measuring current, electronics and installation situation must be assessed together.
Direct replacement is also not readily possible. The evaluation electronics must be expressly designed for the relevant sensor type and the two-, three- or four-wire connection used.
The best solution therefore does not result from the number 100 or 1000 alone. The decisive factors are the cable length, accuracy target, available electronics, temperature range and mechanical design of the complete measuring point.
Frequently asked questions about Pt100 and Pt1000
What is the most important difference between Pt100 and Pt1000?
The Pt100 has a nominal resistance of 100 Ω at 0 °C, while the Pt1000 has a nominal resistance of 1,000 Ω. For the same temperature change, the Pt1000 therefore provides an approximately ten times greater absolute change in resistance.
What does “Pt” mean in Pt100?
Pt stands for platinum. The number indicates the nominal resistance of the sensor at 0 °C.
What resistance does a Pt100 have at 100 °C?
According to the standardised characteristic, the nominal resistance at 100 °C is approximately 138.5 Ω.
What resistance does a Pt1000 have at 100 °C?
The nominal resistance at 100 °C is approximately 1,385 Ω.
Is a Pt1000 ten times more accurate than a Pt100?
No. Its resistance and absolute resistance change are ten times greater. The tolerance class and therefore the permissible sensor deviation can be the same for both types.
Why is the influence of the cable smaller with a Pt1000?
A specific lead resistance represents a considerably smaller proportion of the overall sensor signal with a Pt1000. The resulting calculated temperature error is therefore approximately ten times smaller than with a Pt100.
Is a Pt1000 in a two-wire connection always sufficient?
No. A relevant error can also occur with a Pt1000 when cables are long, thin or exposed to significant temperature changes. The required accuracy and actual lead resistance must be checked.
Why is a Pt100 frequently used in a three-wire connection?
The three-wire connection largely compensates for the lead resistance and requires only one additional conductor. It therefore offers a good compromise for industrial measuring points.
What is required for three-wire compensation?
The resistances of the connecting conductors must be as equal as possible. Different lengths, cross-sections or terminal connections result in a remaining measuring error.
When should a four-wire connection be used?
It is particularly useful for calibration, reference measurements, long cables and high accuracy requirements. The lead resistance is almost completely removed from the measured result.
Can a Pt1000 be connected in a three-wire configuration?
Yes, provided that the sensor and evaluation electronics support a Pt1000 three-wire input.
Can a four-wire sensor be used with a three-wire input?
This is often possible with the appropriate connection. The terminal assignment must comply with the manufacturer’s wiring diagram. The advantages of a genuine four-wire measurement are lost in this case.
Can a Pt100 be connected to a Pt1000 input?
No, not without corresponding reconfiguration of the evaluation electronics. The resistance is ten times too low and would be interpreted incorrectly.
Can a Pt1000 be connected to a Pt100 input?
No. The considerably higher resistance causes an incorrect measured value, measuring-range overflow or a sensor fault indication.
Are Pt100 and Pt1000 mechanically interchangeable?
They may be offered in similar housings, but they do not necessarily have the same dimensions, connections or thermal properties. The mechanical and electrical data must be checked separately.
Which sensor is more widely used in industry?
The Pt100 is particularly widespread in conventional industrial and process applications. Many existing transmitters, controllers and PLC modules are designed for Pt100 as standard.
When is a Pt1000 particularly useful?
A Pt1000 is useful with a two-wire connection, longer connecting cables, compact electronics and existing Pt1000 inputs.
Which sensor is better suited to building automation?
Pt1000 is frequently used because simple two-wire connections are possible and the influence of the cable remains comparatively small. However, the specific controller or automation component must support the sensor.
Which sensor is better suited to calibration technology?
Both Pt100 and Pt1000 can be suitable. The decisive factors are tolerance, stability, sensor design and a genuine four-wire measurement. Pt100 is very widespread in precision and calibration technology.
Does a Pt1000 have a faster response time?
Not fundamentally. The response time is determined mainly by the dimensions, thermowell, thermal contact, medium and installation situation.
Can a Pt100 respond faster than a Pt1000?
Yes. A small Pt100 with good thermal contact can respond considerably faster than a Pt1000 installed in a solid thermowell.
What is self-heating?
The measuring current generates electrical power loss in the sensing element. This can cause the sensor to heat slightly above the actual temperature of the medium.
Is self-heating greater with a Pt1000?
With the same measuring current, the power loss would be greater because of the higher resistance. Suitable Pt1000 inputs therefore normally use a smaller measuring current.
What is Class A for a Pt100?
Class A describes a defined maximum permissible deviation from the standardised characteristic within a specified temperature range. It does not automatically apply to the complete measuring chain.
Are Pt1000 sensors available in Class A or AA?
Yes, depending on the specific sensing element and its permissible temperature range. Availability must be checked for the required sensor version.
Why is a Class A Pt100 still not completely accurate?
In addition to the sensor tolerance, lead resistance, electronics, installation errors, heat conduction and self-heating can influence the measurement.
How can I identify whether a sensor is a Pt100 or Pt1000?
The safest method is to check the type marking or documentation. A resistance measurement at approximately room temperature also provides a clear indication: a Pt100 is in the range of 100 Ω, while a Pt1000 is around 1,000 Ω.
What resistance does a Pt100 have at room temperature?
At approximately 20 °C, the nominal value is around 107.8 Ω. The exact value depends on the actual temperature and sensor tolerance.
What resistance does a Pt1000 have at room temperature?
At approximately 20 °C, the nominal value is around 1,078 Ω.
Can a multimeter test a Pt100?
A resistance measurement enables a basic plausibility and continuity check. A correspondingly accurate measuring system and a known temperature reference are required for an accurate temperature assessment or calibration.
How is a Pt100 input on a PLC tested?
The sensor is disconnected and replaced by a suitable Pt100 simulator or precision resistor. It is then checked whether the PLC displays the corresponding temperature correctly.
Can the same simulator be used for Pt100 and Pt1000?
Only if it expressly supports both characteristics or resistance ranges. A Pt100-only simulator does not automatically generate suitable Pt1000 values.
When should a 4–20 mA transmitter be used?
It is useful with long cables, severe interference, standardised PLC inputs or when diagnostic and configuration functions are required.
Which sensor does a universal RTD transmitter use?
Many modern instruments support both Pt100 and Pt1000. The actual sensor type and connection method must be configured correctly before commissioning.
Can the UPS4E simulate a Pt100 or Pt1000?
The UPS4E is designed for 4–20 mA current loops. It can test the output of a temperature transmitter or the PLC current input, but it does not simulate a Pt100 or Pt1000 resistance.
Which information is required when selecting a resistance thermometer?
The sensor type, connection method, tolerance class, temperature range, insertion length, diameter, process connection, medium, pressure, cable design, cable length, available electronics and any calibration or explosion-protection requirements are required.