A sensor signal conditioning circuit specifically designed for PT1000 resistance temperature detectors.

In modern electronic devices, operational amplifiers are an indispensable component. Particularly in the design of domestically produced op‑amp circuits, selecting appropriate components and optimizing the circuit architecture have become focal points for many engineers. Today, we will delve into the key principles and techniques of designing domestic op‑amp circuits, helping you elevate your circuit‑design expertise. 1. Understand the Basic Characteristics of Operational Amplifiers First and foremost, when designing a domestic op‑amp circuit, it is essential to grasp the amplifier’s fundamental characteristics. The core performance of an op‑amp hinges on parameters such as gain, input impedance, and output impedance. Gain determines the signal‑amplification capability; input impedance affects the source‑load interaction; and output impedance influences the signal‑transmission efficiency. Only by thoroughly understanding these basic traits can we proceed with more effective circuit design. 2. Choose the Right Domestic Operational Amplifier While the market offers a wide array of domestically manufactured op‑amps, not every model is suitable for your specific project. When making your selection, consider several critical factors: bandwidth, power consumption, operating temperature range, and cost. For instance, if your application involves high‑frequency signal processing, bandwidth becomes the primary consideration. Conversely, for projects with stringent low‑power requirements, prioritize low‑power consumption.

I. Overview

　　With the advancement of the Internet of Things, sensors—key components of this ecosystem—have opened up vast prospects for development and are playing an increasingly vital role across diverse industries. As devices for measuring temperature, temperature sensors are widely employed in sectors such as marine engineering, defense, and aerospace. Concurrent with the ongoing push toward industrial automation, demands for precise temperature control and monitoring continue to rise. Accurate temperature sensing enables real-time, high‑precision monitoring of equipment operating conditions, facilitating fine‑tuned adjustments that effectively enhance energy efficiency and reduce energy consumption.

　　Platinum resistance temperature sensors, fabricated from the corrosion‑resistant and chemically stable precious metal platinum, offer high accuracy, excellent stability, superior linearity, a wide measurement range, high sensitivity, and robust reliability, enabling long‑term, dependable operation in harsh environments while delivering highly accurate, low‑distortion temperature measurements. These sensors are widely suited for precision applications in fields such as medical equipment, electric motors, industrial processes, temperature monitoring, satellite systems, meteorology, and resistance‑value calculations, making them exceptionally versatile. Platinum resistance sensors are typically designated by their nominal resistance at 0°C; for example, a PT1000 sensor indicates a nominal resistance of 1,000 Ω at 0°C. In practical applications, a three‑wire connection is commonly employed. Compared with the conventional two‑wire configuration, the three‑wire method provides enhanced immunity to interference introduced by lead‑wire resistance, thereby improving measurement accuracy.

　　In response to current development trends and market demand, Hangjing Company is now introducing the HJPT1000—a dedicated two‑wire current‑loop transmitter designed for PT1000 resistance temperature detectors. This device converts the resistance values of a PT1000 across various temperature ranges into corresponding current outputs. The HJPT1000 employs a thick‑film integrated circuit process compliant with GJB 2438B and features an F14‑02 ceramic surface‑mount package. It is specifically engineered for measuring platinum resistance thermometers (PT1000) and can be customized to meet customer‑specified temperature measurement ranges. A built-in high‑precision current source provides excitation current to the PT1000; this current‑signal excitation method ensures robust immunity to interference over input lead lengths, thereby enhancing measurement accuracy. The HJPT1000 boasts high precision, low power consumption, two‑wire current output, and a wide supply voltage range, satisfying direct aviation‑grade voltage‑supply requirements. Its current‑output characteristic also confers strong capabilities for long‑distance transmission and effective rejection of electromagnetic noise, enabling it to withstand extreme environmental stresses and harsh electromagnetic conditions. As a result, its application scope is significantly broadened. Key features are as follows:

　　It can acquire and process signals from three-wire RTDs while providing a two-wire 4–20 mA current output.

　　The power supply voltage supports direct operation from 18 to 36 V, enables long‑distance transmission, and offers strong anti‑interference performance.

II. Electrical Principle Block Diagram

 

 

III. Package Type and Lead Terminal Functions

1. Package Type

Figure 2: Dimensional Drawing of the F14-02 Housing

 

 

Figure 3: Physical specimen of HJPT1000 and its reference image

2. Lead-out Terminal Functionality

Table 2: Functional Table of Package Lead Pins

 

Pin number	Symbol	Functionality	Pin number	Symbol	Functionality
1	IREF	Reference Current Output Terminal	14	+VS	Positive power supply
2	RSET2	Reference Current Setting Terminal	13	NC	Empty foot
3	NC	Empty foot	12	IOUT	Current output terminal
4	FGND	Floating ground	11	RSET1	Resistance setting terminal
5	IN	Signal Input	10	TP2	Output Current Setpoint 2
6	NC	Empty foot	9	TP1	Output Current Setpoint 1
7	NC	Empty foot	8	BYPASS	Compensation Capacitor Configuration

  

IV. Electrical Characteristics

Unless otherwise specified, +V _S =+28V, T _A =25℃

Table 3 Electrical Characteristics Table

Parameter Name	Symbol	Test conditions		Standard value			Unit
				Minimum value	Typical value	Maximum value
Output low-side current	IOL			3.9	4	4.1	mA
Output high-end current	IOH			19.5	20	20.5	mA
Output current Temperature drift coefficient*	αIset	Iset = 4 mA -55℃ to +125℃			70	100	ppm/°C
Nonlinearity*					0.5	1	%
Supply current	IS	VIN=0V			2	2.5	mA
			-55℃ to +125℃		2.6	3.3
Power supply voltage range	+VS			18		36	V

Note: Parameters marked with an asterisk are design guarantees.

 

V. Typical Application Diagrams

Figure 4: Typical Application Diagram for the HJPT1000 Three-Wire System

Note:

1. Note that the FGND pin of the HJPT1000 serves as the system’s floating ground, not the ground of the supply voltage +VS. The current output IOUT should be connected to the supply voltage’s ground via a sampling resistor.

2. Resistors R1, R2, RSET1, and RSET2 should all be selected with a tolerance of 0.1% to ensure the overall system’s measurement accuracy. The external components shown in the diagram are chosen such that, within an ambient temperature range of –55°C to +200°C, the RTD can deliver an output current of 4–20 mA.

3. In high‑current applications, such as a 20 mA current output, the device’s overall thermal power dissipation can become significant. To reduce power consumption, an external resistor RP can be connected between the remote positive supply and pin 14 of the device, thereby lowering the voltage drop across the device. However, care must be taken to ensure that the resistor value is not excessively large; if it is too high, the voltage difference between the collector and emitter of the internal transistor will decrease, potentially driving the transistor into saturation. In this case, the output current would vary with changes in the supply voltage, losing its stability.

4. When acquiring and processing the output current after long‑distance transmission, it is recommended that customers refer to the typical application diagram and connect a 1 µF capacitor CO in parallel with the termination resistor RO. This capacitor effectively reduces power‑line frequency interference, thereby smoothing the output current signal. Note that increasing the capacitor value reduces output current noise; however, the time constant τ of the RO–CO network also increases, leading to a longer settling time for the output signal. In practical applications, users should select the capacitor value appropriately based on their specific requirements for signal noise and settling time.

5. Due to the thermal‑junction‑temperature characteristics of the device, the HJPT1000 must not be operated in an ambient temperature exceeding TA ≥ 140°C.

6. Although the device’s power supply and output can accommodate long‑line transmission, its input cannot accept long‑line signals; therefore, we recommend that, when in use, the transmission line between the PT1000 and the device’s input not exceed 50 cm.