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Aug 3, 2024, 12:49:43 AM8/3/24

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The Time Electronics 1090 is a precision portable process calibrator that combines source and measurement functions for thermocouples, PT100s, V, mV & mA. As a multifunction instrument the 1090 combines accuracy and durability with simple operation, making it ideal for process plant applications.

The Time Electronics 1090 process calibrator is able to measure and simulate the temperature and mV characteristics of J, K, T, R, S, B, N and E thermocouples and can operate with or without internal cold junction compensation. The 1090 also measures and simulates PT100, based on 0.3850 alpha probe standard, over a range of -200C to 700C. The display can be easily changed from C to F. The equivalent uV (thermocouples) and ohms (PT100) can also be shown.

The Time Electronics 1090 process calibrator has measurement ranges of 0 to +/-30mV and 0 to +/-60mA and source ranges are 0 to +/-80mV and 0 to +80mA. The 1090 has a general-purpose inching function. This adjusts the output in fixed increments of temperature (thermocouples only) or voltage or current. The set-up menu gives a the user a choice of three levels of increment i.e. 0.1, 1 or 10 for C/F, or 1, 10, or 100 uV/uA for voltage/current. The lowest of these represents the highest setting resolution and provides the most precise control of the output. This is especially useful for calibrating thermostat controllers that have tight specification on hysteresis.

Up to 10 values can be stored in the 1090's non-volatile memory and they can be recalled at any time. The user can also manually step through them in sequence using the step key. Continuous stepping (auto-step) is also available at any user selectable rate between 1 & 10 seconds/step.

Power is via an internal high capacity rechargeable metal hydride battery that can be recharged from the supplied external mains charger. An auto power-down feature helps conserve battery life by switching off the instrument if inactive for over 5 minutes. This feature can be disabled if not required.

The 1090 is a precision portable process calibrator that combines source and measurement functions for thermocouples, Pt100s, V, mV & mA. It is a multifunction instrument that combines accuracy and durability with simple operation, making it ideal for process plant applications and field testing work.

Thermocouple Measurement and Simulation: Measure and simulate the temperature and mV characteristics of J, K, T, R, S, B, N and E thermocouples. The 1090 can be operated with or without internal cold junction compensation.

Features include an increment/decrement function that adjusts an output in fixed increments of temperature (for thermocouples), voltage or current. Three levels of increment are 0.1/1/10 for C/F, or 1/10/100 μV/μA for voltage or current. Lower increments mean higher setting resolution, enabling a more precise control of the output. This is useful when calibrating thermostat controllers that have tight specifications on hysteresis.

Further features are the memory recall and stepping functions. Up to 10 values can be stored and recalled at any time. The user can manually step through them in sequence or use continuous stepping (auto-step) at a selectable rate between 1 & 10 seconds/step.

The 1090 is a robust instrument used for field calibration work. It is supplied with a leather carry case that serves to protect the calibrator and features a folding front cover that enables full usage of the unit when housed.

The 1090 is a versatile multifunction field calibrator for testing and calibration of industrial process equipment. It can be used to measure a temperature sensor output to verify performance, or simulate sensor outputs at different temperatures to check transmitters and measuring devices.

In addition to thermocouple and RTD transmitter calibration, the 1090 provides a solution for process loop diagnostics, fault finding and maintenance. Troubleshoot 4-20 mA loops with mA measurement of a transmitter output, simulate a transmitter with mA source, and provide 24 V loop power.

The circuit can process up to four independent thermocouple channels, and the software linearization algorithms support eightdifferent types of thermocouples (B, E, J, K, N, R, S, and T). Thefour thermocouples can be connected in any combination, andresistance temperature detectors (RTDs) on each thermocouple channel provide cold junction compensation (CJC). No extracompensation is needed. Thermocouple measurements usingthis system cover the full operating range of the various types of thermocouples.

The circuit interfaces to the EVAL-ADICUP360 Arduino-compatible platform for rapid prototyping. With a USB to UART interface and open source firmware, the EVAL-CN0394-ARDZand EVAL-ADICUP360 combination can be easily adapted to avariety of thermocouple applications.

Thermocouples are one of the most frequently used sensors fortemperature measurements in industrial applications because of their low cost, ruggedness, repeatability, as well as wide operating temperature range and fast response time. Thermocouples areespecially useful for making measurements at high temperatures (up to 2300C for Type C thermocouples).

The voltage generated by a thermocouple must be converted to temperature. Converting the voltage measured to an accurate temperature can be difficult, because the thermocouple voltage is small, the temperature-voltage relationship is nonlinear, and the cold junction temperature must also be accurately measured.

The total output voltage of the thermocouple is caused by the difference between the temperature of the thermocouple and the cold junction temperature. Figure 2 shows that the cold junction temperature is measured with another temperature sensitive device, typically a thermistor, diode, RTD, or semiconductor temperature sensor. The temperature-sensing device used for this circuit is a Pt1000 RTD, and there is one RTD in each of the four channels for accurate measurements.

A constant current source, IEXE (obtained from the ADucM360) drives the series combination of the RTD and a precision 1.6 kΩ reference resistor, R5. The IEXE setting for the CN-0394 circuit is 620 μA that produces a nominal VREF of 1.6 kΩ 620 μA = 0.992 V, and a drop of 1 kΩ 620 μA = 0.62 V across the RTD. The voltage across R5 is used as a reference to the ADC. The RTD resistance, RRTD, is calculated using the following equation:

In the CN-0394 circuit, the thermocouple voltage and the RTD voltage are both converted by the ADuCM360 24-bit ADCs. Note that the measurement is ratiometric and not dependent on the accuracy of either the reference voltage or the value of the IEXE excitation current.

The RTD resistance, RRTD, is then converted into the cold junction temperature, TCJ, using either a lookup table or polynomial equations. The RTD transfer function known as the Callender-Van Dusen equation is made up of two distinct polynomial equations to provide a more accurate result and is used in the CN-0394 software. Refer to the Circuit Note CN-0383 for a more detailed explanation of these RTD equations.

The cold junction temperature, TCJ, is then converted into the corresponding thermocouple voltage, VCJ, using the equations in the ITS-90 Thermocouple Database. The CN-0394 software uses the ITS-90 polynomial equations rather than the lookup tables to perform this conversion.

For the thermocouple theory, linearization tables, equations, and cold junction compensation, refer to the NIST ITS-90 Thermocouple Database, NIST Standard Reference Database 60, Version 2.0 (available on the NIST website). For the general theory of thermocouples and temperature measurements, see Chapter 7 of Sensor Signal Conditioning.

The CN-0394 circuit uses the ADuCM360 integrated, dual, 24-bit, Σ-Δ ADC to perform the conversions. The ADuCM360 contains an input multiplexer and an integrated PGA with gain options of 1 to 128. The ADuCM360 can be configured to have 6 differential inputs or 12 single-ended inputs.

The PGA allows amplification of the small thermocouple voltage to a level that is optimum for the internal sigma-delta ADC. The proper gain setting is determined by the amplitudes of the thermocouple signals and the value of the reference voltage. The CN-0394 software supports eight types thermocouple: B, E, J, K, N, R, S, and T.

The cold junction temperature range is 0C to 50C, and the maximum and minimum output voltage range is determined by examining the voltage swings of the various types and including the cold junction voltage component that is subtracted from the thermocouple voltage. The Type E thermocouple requires the widest range, as shown in Table 1.

The ADuCM360 ADC bipolar differential input range using the internal 1.2 V reference is 125 mV with the PGA gain set to G = 8. This range covers the output voltage ranges of all eight types of thermocouples, therefore no external signal conditioning circuits are needed, and the PGA can operate at a fixed gain of 8 for all thermocouple types. The 24-bit resolution allows thermo-couples with small signal ranges (such as Type B) to be measured without the need for gain ranging. The thermocouple is connected in the differential mode to the ADC, and the negative input is connected to a 900 mV common-mode bias voltage supplied by the ADuCM360.

The EVAL-CN0394-ARDZ board has four miniature Type U female thermocouple connectors (Omega PCC-SMP-U-100) for connecting to the thermocouples mating male connectors. The cold junctions are formed at the connector contacts, and the CJC RTDs are located close to the connectors.

A simple 2-wire RTD connection is used in the CN-0394 circuit; however, the ADuCM360 contains programmable excitation currents that can be used for 2-wire, 3-wire, and 4-wire RTDs. Details on 3-wire and 4-wire applications can be found in Circuit Note CN-0383, respectively.