Spider-80Ti Temperature Measurement System
The Spider-80Ti is a front-end from the Spider-80Xi hardware platform that enables temperature measurement. Spider-80Ti supports temperature measurements from Thermocouples and RTD (Resistance Temperature Detector) sensors.
Each Spider-80Ti front-end adds 16 temperature measurement channels to the Spider-80Xi system. A Spider-80Ti front-end is user-configurable to support either a PT100 RTD sensor or a K-type Thermocouple. A combination of RTDs and thermocouples within the same Spider system can also be achieved by combining the front-ends configured as RTDs and Thermocouples.
Spider-80Ti is equipped with a 24-bit Sigma-Delta Analog to Digital Converter (ADC) per channel to ensure highly accurate temperature measurements with any type of sensor. Together with the user-configurable non-linearity correction, the accuracy of the measurements is ensured over a wide range of temperature measurements.
The Spider-80Xi chassis can either be configured exclusively for temperature measurements using the Spider-80Ti front-end or can be configured for mixed signal data acquisition by combing the Spider-80Ti with Spider-80Hi, Spider-80Ci, or Spider-80SGi. A choice of Spider 80Xi chassis with 4 front-end slots or 8 front-end slots is available.
The efficient design of the Spider-80Xi chassis eliminates individual enclosures for each modular front-end to minimize the overall dimensions of the system. Its lightweight makes it ideal for applications requiring portability and an efficient size without the need to exchange front-ends during operation.
Spider-80Ti Setup
Multi-module setup
Multiple chassis consisting Spider-80Ti front-ends or a combination of Spider-80Ti, Spider-80Hi, Spider-80Ci, or Spider-80SGi can be chained together to form a system with up to 1024 channels, all sampled simultaneously.
The Spider-80Xi system is equipped with powerful and flexible data acquisition functions. Users can initiate continuous time data recording or data recording triggered by user configurable events including pre-set run schedule, alarm limit trigger, input trigger, or digital input trigger. A high-performance removable 2.5-inch solid-state drive (SSD) is used as a storage media inside Spider-80Xi. The default capacity of the SSD is 250 GB and is extendable up to 2 TB. When recorded, data will be written in the NTFS file format. Data is extracted from the SSD using Crystal Instruments PC software to transfer data to the PC, or the SSD can be physically removed and connected to another PC.
Terminology
Maximum and minimum specifications characterize the warranted performance of the instrument within the recommended calibration interval and under the stated operating conditions. These specifications are guaranteed by design.
Typical specifications would be met by the instrument within the recommended calibration interval at the specified operating conditions. These measurements are taken during production verification of the finalized engineering prototype. The performance of the instrument is not warranted.
All performance specifications are typical unless otherwise noted. These specifications are valid within the full operating temperature range. Accuracy specifications are valid within ±5 °C after calibrating the unit unless otherwise noted.
Selection of Temperature Sensors
The Spider-80Ti front-end supports the two widely used sensors, the PT100 RTD sensor and K-type thermocouples making it ideal for temperature measurements. Some of the key differences that aid in selecting a sensor for an application is listed below:
| Sensor Type | RTD | Thermocouple |
|---|---|---|
| Temperature Range (typical) | -200 to 650°C | 200 to 1750°C |
| Accuracy (typical) | 0.1 to 1°C | 0.5 to 5°C |
| Long-term Stability | Good | Variable |
| Stable and repeatable | Drifts because of oxidation | |
| Linearity | Fairly linear | Non-linear |
| Power Required | Constant voltage or current | Self-powered |
| Reference Junction | Not Required | Required |
| Response Time | Generally slow | Fast |
| 1 to 10s | 0.10 to 1s | |
| Susceptibility to Electrical Noise | Less Susceptible | More Susceptible |
| Cost | High | Low |
A majority of RTDs are designed for typically designed for measurements up to 500o C whereas thermocouples can operate at significantly higher and wider temperature ranges. Based on the table and measurement condition the appropriate sensor can be used. With 2 or more front-end modules both types of sensors can be used (1 sensor type per module).
Environmental and General Spider-80Xi Specifications
For details on Environmental and General Specifications of the Spider-80Xi system and chassis, please request the “Spider Front-End Hardware Specifications for Spider-80Xi Platform: Spider-80Hi, 80Ci, 80SGi, and 80Ti”
Spider-80Ti with RTD Sensor
RTD Measurement Circuit
In the 3- Wire RTD sensor, two wires link the sensing element to the Spider-80Ti on one side of the sensing element, and one links it on its other side as shown in the picture below.
The Spider then calculates the compensation based on the following principle, if three identical type wires are used and their lengths are equal, then R1 = R2 = R3. By measuring the resistance through leads 1, 2, and the resistance element, a total system resistance is measured (R1 + R2 + RE ).
If the resistance is also measured through leads 2 and 3 (R2 + R3), the resistance of only the lead wires is measured, and since all lead wire resistances are equal, subtracting this value (R2 + R3) from the total system resistance (R1 + R2 + RE) which eliminates any lead wire error, providing an accurate temperature measurement.
Each RTD channel is passed through a programable gain amplifier and then sampled by a 24-bit analog-to-digital converter (ADC). Finally, a user customizable moving linear average is applied to the measurements.
Spider-80Ti RTD Specifications
| Number of Input Channels | 16 channels per front-end Expandable up to 1024 channels |
|---|---|
| Connector Type | Six pins pluggable terminal blocks (Each block connects two input channels) |
| ADC | 24-Bit Sigma - Delta |
| Temperature Measurement Range | -200°C to 850°C (-328°F to 1562°F) |
| Resistance Measurement Range | 0 to 400 W |
| RTD Excitation Current Source | 10 μA to 1.5 mA programable source |
| Operating Temperature | -10°C to 55°C (14 oF to 131°F) |
| Normal-mode Rejection Ratio (50/60 Hz) | 105 dB |
| Common Mode Rejection Ratio (CMRR) | 115 dB |
| Differential Input Impedance | 2 MΩ |
| Channel-to-COM | ±3 V |
| Sampling Rate | 0.3125, 0.625, 1.25, 2.5… 512 S/sec (user selectable) |
| Average Number and Mode | User selectable moving linear average from 1 – 64 |
RTD Temperature Measurement Accuracy
RTD Non-Linearity Correction
To provide high accuracy during measurements the Spider-80Ti directly implements the IEC 751 RTD equations, the user can choose to use the coefficient values as defined by the standard or specify custom coefficients. Having these customizable coefficients also allows the user to use RTD sensors with different alpha values and greatly improves the accuracy of the measurements.
RTD Operating Measurement Accuracy
The following figures show the errors for RTDs and thermocouples on the Spider-80Ti. The figures display the errors over a full temperature range at room temperature. The figures account for gain errors, offset errors, differential, and integral nonlinearity, quantization errors, noise errors, and lead wire resistance. The figures do not account for the accuracy of the sensor itself.
RTD Channel Gain and Offset Calibration
Gain and offset error may be introduced due to the source impedance of the sensor or other factors. Sensors with higher lead resistance may introduce significant errors. Spider-80Ti has an built-in function to perform gain correction and offset nulling for each individual channel to negate these errors.
Spider-80Ti with Thermocouples
Thermocouple Measurement Circuitry
Each thermocouple channel is passed through a programable gain amplifier and then sampled by a 24-bit analog-to-digital converter (ADC). Then the cold junction compensation and a user customizable moving linear average is applied to the measurements.
Cold Junction Compensation
Thermocouples have two junctions, namely the Hot and Cold Junction. The hot junction is the measurement junction and is attached to the measurement point. In theory, the cold junction should be maintained at 0°C. As this is not a practical solution the cold junction is connected to an Isothermal block, the temperature of this block is measured by a high precision internal temperature sensor.
The thermoelectric voltage across the sensor is measured. The internal sensor measures the isothermal temperature, this is then converted to its corresponding voltage value. This value is used to offset the cold junction temperature to provide an accurate measurement.
Spider-80Ti Thermocouple Specifications
| Number of Input Channels | 16 channels per front-end Expandable up to 1024 channels |
|---|---|
| Connector Type | Six pins Pluggable Terminal Blocks (Each block connects two input channels) |
| ADC | 24-Bit Sigma -Delta |
| Temperature Measurement Range | -270°C to 1250°C (NIST – K type) |
| Voltage Measurement Range | ±80 mV |
| Operating Temperature | -10°C to 55°C (14°F to 131°F) |
| Cold Junction Compensation Accuracy | +/- 0.25°C (0°C to 70°C) |
| +/- 0.75°C (-40°C to 70°C) | |
| Normal-mode Rejection Ratio | 105 dB |
| Common Mode Rejection Ratio (CMRR) | 115 dB |
| Differential Input Impedance | 2 MΩ |
| Channel-to-COM | ±3 V |
| Sampling Rate | 0.3125, 0.625, 1.25, 2.5… 512 S/sec (user selectable) |
| Average Number and Mode | User selectable moving linear average from 1 – 64 |
Thermocouple Temperature Measurement Accuracy
Thermocouple Operating Measurement Accuracy
The following figures show the errors for thermocouples on the Spider-80Ti. The figures display the maximum errors over a full temperature range and typical errors at room temperature. The figures account for gain errors, offset errors, differential and integral nonlinearity, quantization errors, noise errors, lead wire resistance, and cold-junction compensation errors. The figures do not account for the accuracy of the thermocouple itself.
Thermocouple Channel Gain and Offset Calibration
Gain and offset error may be introduced due to the source impedance of the sensor or other factors. Sensors with higher lead resistance may introduce significant errors. The Spider-80Ti has an inbuilt function to perform gain correction and offset nulling for each channel to negate these errors.
Multi-point Sensor Correction
The Spider-80Ti system allows the user to perform multi-point correction if the user has more precise values for the sensor, this data can be entered into the system to provide a linearized offset correction between the temperature breakpoints.