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发布时间：2026/7/22 8:29:53关注度：135
什么是监测继电器？监测继电器是一种安装在DIN导轨上的设备（宽度通常为17.5至22.5毫米），用于持续监测某项电气或物理量（如电压、电流、相序、液位或温度）。它依据IEC 60255标准，将监测值与带有迟滞（hysteresis）特性的可调阈值进行比较；当监测值超出设定范围时，继电器会切换其单刀双掷（SPDT）或双刀双掷（DPDT）输出触点。该设备本身不承载或切断负载电流，而是通过输出信号驱动接触器线圈、PLC输入端或报警电路；因此，如果阈值设置不当或缺少跳闸延时，可能会导致未能检测到实际故障，或者引起本应正常运行的电机发生误跳闸。本文将探讨该设备内部的“检测-比较-切换”回路，解析阈值、迟滞和跳闸延时的作用，介绍继电器监测的主要参数及“故障安全”（fail-safe）输出逻辑的特性，并说明其在控制柜内介于接触器与PLC之间的位置关系。
What is a monitoring relay? A monitoring relay is a DIN-rail device, usually 17.5-22.5 mm wide, that continuously measures one electrical or physical quantity — voltage, current, phase sequence, level, or temperature — compares it to an adjustable threshold with hysteresis per IEC 60255, and switches an SPDT or DPDT output contact when the quantity leaves the set window. It does not carry or interrupt load current itself; the output drives a contactor coil, a PLC input, or an alarm circuit, so a wrong threshold or a missing trip delay either lets a real fault through or nuisance-trips a motor that was running fine. This article covers the sensing-compare-switch loop inside the device, what threshold, hysteresis, and trip delay each do, the main quantities these relays measure, how fail-safe output logic behaves, and where the relay sits between a contactor and a PLC in a panel.
包含三个阶段，且始终按此顺序进行。第一阶段是检测：利用分压器直接读取线路电压，利用分流器或电流互感器读取电流，利用电极对读取电导率以监测液位，或利用 PTC/PT100 传感器读取绕组电阻以监测温度。第二阶段是比较：内部比较器电路将测量值与设定值（通过旋钮或 DIP 开关设定）进行持续比对；这种比对是实时进行的，不同于 PLC 输入模块那种基于扫描周期的运作方式。第三阶段是输出：当测量值越过阈值并持续超过该阈值达到设定的动作延时（trip delay）后，继电器线圈动作，从而使转换触点进行断开或闭合切换。
电源需求因功能而异。例如 ABB CM-MPS 或施耐德 Zelio RM17TE 等三相电源监测继电器，其自身的工作电源直接取自被监测的三相线路，无需额外的 24V 或 230V 电源，从而简化了启动器控制柜的接线。而单功能的电压、电流、液位及温度监测继电器通常需要独立的辅助电源。接线前请务必查阅产品数据手册；在需要辅助电源的设备上误以为其具备自供电功能，是首次调试时常见的错误。
Three stages, always in this order. First, sensing: a voltage divider reads line voltage directly, a shunt or current transformer reads current, a pair of electrodes reads conductivity for level, or a PTC/PT100 sensor reads winding resistance for temperature. Second, comparison: an internal comparator circuit checks the measured value against the setpoint dial or DIP-switch selection, continuously, not on a scan cycle like a PLC input card would do it. Third, output: when the value crosses the threshold and stays past it for the trip delay, the relay coil switches, and the change-over contact opens or closes.
Power source varies by function. Three-phase supply monitors such as the ABB CM-MPS or Schneider Zelio RM17TE draw their own operating power from the measured three-phase lines — no separate 24V or 230V feed needed, which simplifies wiring on a starter panel. Single-function voltage, current, level, and temperature relays typically need a separate auxiliary supply. Check the datasheet before wiring; assuming self-powered operation on a unit that needs an aux feed is a common first-commissioning mistake.
监测继电器的运行特性由三个可调参数决定；若其中任何一个设置不当，都可能导致故障漏检或误动作。阈值是触发输出切换的设定值（可以是过限、欠限或包含上下限的窗口值）。迟滞是指阈值下方（或上方）的复位区间；若无迟滞，当读数在设定点附近波动时，输出信号便会发生频繁的通断切换（抖动）。动作延时是指故障状态必须持续的时长，只有超过该时长后输出才会实际切换；这使得继电器能够“穿越”短暂的电压跌落或电机启动浪涌电流，而不会发生误动作。
公式：迟滞复位阈值 —— 来源：IEC 60947-5-1 标准中的切换差值（switching-differential）概念
Vreset = Vtrip × (1 - H%)
Three adjustable parameters define how a monitoring relay behaves, and getting any one of them wrong causes either a missed fault or a nuisance trip. The threshold is the value at which the output switches — over, under, or a window with both limits. Hysteresis is the reset band below (or above) that threshold; without it, a reading that hovers exactly at the setpoint makes the output chatter on and off. Trip delay is the time the fault condition must persist before the output actually switches, which lets the relay ride through a brief sag or a motor inrush without tripping.
Formula: Hysteresis Reset Threshold — Source: switching-differential concept per IEC 60947-5-1
Vreset = Vtrip × (1 - H%)
迟滞（Hysteresis）是指动作值与复位值之间的差值（通常以阈值的百分比表示）；设置迟滞是为了防止当被测物理量在设定值附近波动时，输出继电器发生频繁的“抖动”（chattering）或误动作。
跳闸延时（Trip delay）是指故障状态必须持续的最短时间，只有超过该时间，输出继电器才会动作；它能滤除那些无关紧要的瞬态干扰，例如邻近电机启动时引起的电压暂降。
关键要点： 迟滞设置较小（复位区间窄）时响应速度快，但在阈值附近发生抖动的风险较高；迟滞设置较大时系统更稳定，但会导致复位前的数值漂移幅度更大。应根据具体负载情况进行调整，而不应盲目沿用出厂默认值。
现场观察： 安装人员往往将动作延时保持在出厂最小值，结果因同一馈线上其他设备产生的正常切换瞬态干扰，导致系统频繁发生误动作（滋扰性跳闸），不得不耗费数周时间排查问题。对于三相电源监测设备，将延时从 0.1 秒增加到 1–3 秒通常就能解决这一问题，代价仅仅是对真正的缺相故障响应稍慢一些。
Hysteresis is the gap between the trip value and the reset value, expressed as a percentage of the threshold, that prevents the output relay from chattering when the measured quantity sits near the setpoint.
Trip delay is the minimum time a fault condition must be present before the output relay switches; it filters out transients that are too brief to matter, such as a voltage dip during a neighboring motor start.
Key takeaway: A tight hysteresis (a narrow reset band) gives fast response but more chatter risk near the threshold; a wide hysteresis is stable but leaves a bigger gap where the quantity has already drifted before the output resets. Match it to the load, not the factory default.
What we see in the field: installers leave the trip delay at its factory minimum and then chase nuisance trips for weeks on a supply with normal switching transients from other equipment on the same feeder. Bumping the delay from 0.1 s to 1-3 s on a three-phase supply monitor usually clears it, at the cost of a slightly slower response to a genuine phase loss.
六类监测参数涵盖了几乎所有的应用场景。三相电源及相序继电器可在单一设备内监测相位的存在、相序（旋转方向）、缺相以及通常包含的电压不平衡情况——若电机启动时相序错误会导致反转，因此这些继电器会在接触器闭合前阻止启动（详见“相序与缺相继电器”相关内容）。电流监测器通过分流器或外部电流互感器（CT）检测过电流（如卡滞）或欠电流（如皮带断裂、水泵空转、负载丢失）状况。
液位监测器利用电极间的导电感应实现泵的启停控制及空转保护，并提供千欧（kΩ）级的灵敏度调节，以适应不同液体的导电率。温度监测器可读取嵌入电机绕组中的PTC热敏电阻（符合IEC 60947-8标准）信号，或使用PT100/PT1000传感器获取实际温度读数并进行设定值控制。绝缘监测设备（符合IEC 61557-8标准）属于独立类别：在不接地（IT）系统中，它们持续监测对地绝缘电阻，并在发生第一次故障时即发出警报，从而在第二次故障引发危险前提供保护——这是医院医疗IT系统的标配，也常见于船舶和工业流程工厂。
关键提示：应根据需要监测的参数而非控制柜的可用空间来选择继电器。三相电源监测器无法检测水泵空转，液位继电器也无法检测相序反接——组合使用多种单功能继电器是常规做法，并非过度设计。
Six quantities cover almost every application. Three-phase supply and phase-sequence relays check phase presence, rotation, loss, and usually asymmetry in one device — wrong rotation on a motor start means it runs backwards, so these relays block the start before the contactor closes; see phase sequence and phase failure relays for the detail. Current monitors catch overcurrent (a jam) or undercurrent (a broken belt, a dry pump, a lost load) through a shunt or an external CT.
Level monitors use conductive sensing between electrodes for pump up/down control and dry-run protection, with adjustable sensitivity in kOhm to match the liquid's conductivity. Temperature monitors read a PTC thermistor embedded in a motor winding per IEC 60947-8, or a PT100/PT1000 for an actual temperature readout with a set point. Insulation monitoring devices, per IEC 61557-8, are a separate category: in an unearthed IT system they measure insulation resistance to earth continuously and alarm on the first fault, before a second fault becomes dangerous — standard in hospital medical IT systems and common in marine and process plants.
Key takeaway: Pick the relay by the quantity you need to catch, not by the panel space available. A three-phase supply monitor will not catch a dry-running pump, and a level relay will not catch reversed phase rotation — stacking single-function relays is normal, not a sign of over-engineering.
这是两个独立的选项，通常在继电器上进行设置或通过接线方式确定。常带电（故障安全）输出逻辑意味着继电器线圈在正常运行时保持通电，而在发生故障或辅助电源丢失时断电——对于下游电路而言，断电的继电器与触发动作的继电器状态一致，这正是安全相关联锁系统所期望的特性。常不带电逻辑则与之相反，适用于不希望输出在正常条件下持续带电的场合，例如为了减少发热或降低线圈磨损的设计。
故障安全（常带电）输出是指继电器线圈在正常条件下保持通电的逻辑；因此，任何电源丢失或实际故障都会导致线圈断电，从而使下游电路进入安全状态。
复位方式是第二个选项：自动复位是指一旦测量值恢复至回差（hysteresis）范围之外，输出即自动恢复就绪状态；而手动（锁存）复位则要求即使故障已排除，仍需操作人员确认后才能解除触发状态。在无人值守重启前需要操作人员先检查设备的场合（例如无人值守生产线上的泵空转或缺相故障），采用锁存复位是正确的选择。
关键要点：对于无人值守情况下的自动重启可能导致设备损坏或产生危险的场合，应指定采用故障安全且锁存复位的逻辑。仅在“误动作导致的停机”所带来的影响重于“无人值守重启风险”的情况下，才考虑使用自动复位。
Two independent choices, both set at the relay or by wiring convention. Normally-energized (fail-safe) output logic means the relay coil is energized during normal operation and de-energizes on a fault or on loss of its own auxiliary supply — a dead relay looks the same as a tripped relay to the downstream circuit, which is what you want on a safety-relevant interlock. Normally-de-energized logic inverts that, and is used where holding the output continuously energized under normal conditions is undesirable, for example to limit heat or coil wear in some designs.
Fail-safe (normally-energized) output is an output logic where the relay coil stays energized under normal conditions, so any loss of supply or genuine fault de-energizes it and drives the downstream circuit to its safe state.
Reset behavior is the second choice: automatic reset re-arms the output as soon as the measured value returns past the hysteresis band, while manual (latched) reset holds the tripped state until an operator acknowledges it, even after the fault clears. Latching is the right call where a fault needs an operator to look at the machine before it restarts unattended — a dry-running pump or a phase-loss event on an unmanned line, for instance.
Key takeaway: Specify fail-safe, latched-reset behavior for anything where an unattended automatic restart could damage equipment or create a hazard. Specify auto-reset only where nuisance downtime matters more than the risk of an unattended restart.
监测继电器的输出触点仅用于传输信号，而非承载主回路功率。若将其连接至接触器线圈，它可直接切断接触器——这种方式常见于电机启动器中，用于在发生缺相或过压等故障时立即停止电机，而无需等待 PLC 逻辑处理。若将其连接至 PLC 数字量输入端，该信号便成为控制程序中的一个数据位，使 PLC 能够在采取动作前记录事件、执行顺序停机或触发 HMI 报警。若将其与电机保护断路器并联接入跳闸回路，则可提供断路器自身热磁或电子脱扣单元无法监测的参数（如相序或绝缘电阻）。
具体选择取决于控制柜的整体架构：硬接线的接触器互锁响应速度更快，且在 PLC 故障或程序停止时仍能有效工作；而 PLC 输入方式则提供了更好的可观测性，并允许在无需重新接线的情况下修改响应逻辑。大多数控制柜制造商会同时采用这两种方案：通过接触器线圈实现硬接线的安全相关跳闸，同时向 PLC 发送并行信号以进行记录并在 HMI 上显示。关于触发跳闸的设定参数，请参阅监测继电器中的“迟滞（hysteresis）”、“跳闸延时（trip delay）”和“自保持（latching）”功能；
The monitoring relay's output contact is a signal, not a power path. Wired to a contactor coil, it blocks or drops the contactor directly — common on motor starters where a phase-loss or overvoltage condition must stop the motor without waiting on PLC logic. Wired to a PLC digital input, it becomes one bit in the control program, letting the PLC log the event, sequence a shutdown, or trigger an HMI alarm before acting. Wired into a trip circuit alongside a motor protection circuit breaker, it adds a measurement the breaker's own thermal-magnetic or electronic trip unit does not cover, such as phase sequence or insulation resistance.
This depends on how the rest of the panel is built: a hard-wired contactor interlock reacts faster and survives a PLC fault or program stop, while a PLC input gives visibility and lets the response logic change without rewiring. Most panel builders run both — a hard-wired safety-relevant trip through the contactor coil, and a parallel signal to the PLC for logging and the HMI. For the settings behind that trip decision, see hysteresis, trip delay and latching in monitoring relays.
监测继电器会切断主电源回路吗？
不会。其输出触点属于信号级单刀双掷（SPDT）或双刀双掷（DPDT）触点，用于驱动接触器线圈、PLC 输入端或报警装置；它不具备直接切换电机或馈线电流的额定能力。
监测继电器与保护继电器有何区别？
两者均遵循 IEC 60255 标准，但保护继电器是根据保护等级要求制造的，旨在利用协调的时间-电流特性曲线切断馈线和电机上的故障电流路径；而监测继电器则针对单一参数进行监测，将其与可调阈值进行比较，并切换低功率输出。虽然 PLC 可以通过软件实现部分监控功能，但它无法提供专用继电器那种基于硬接线且独立于主电源的响应特性。
为什么监测继电器需要独立的辅助电源？
大多数针对电压、电流、液位或温度的单功能监测器都需要控制电压（通常为 24V DC 或 230V AC）来为内部电子元件供电。三相电源监测器和相序监测器是主要例外——许多此类设备直接从被测线路获取工作电源。
监测继电器中的“迟滞”（Hysteresis）起什么作用？
迟滞设定了动作值（跳闸值）与复位值之间的差值。如果没有迟滞，当读数恰好处于阈值附近时，输出继电器会发生频繁的吸合与释放（抖动）；若正确设置了迟滞，输出状态将保持不变，直到监测参数明显恢复并越过复位区间。
应该选择自动复位还是手动复位？
对于无人值守情况下的重启可能导致设备损坏或产生危险的故障（例如水泵空转，或缺相跳闸后的无人值守生产线），应选择手动（锁定）复位。如果更担心非必要的停机，且故障状况可自行消除（例如短暂的电压瞬变），则应选择自动复位。
单个监测继电器能否同时监测电压和电流？
部分多功能型号可以实现这一点——例如施耐德（Schneider）的 RM35TF 及类似的高端系列产品，将多种监测参数集成在 22.5 至 45 毫米宽的外壳内。不过，在不受限于控制柜空间或系统复杂性的情况下，单功能继电器仍然更为常用。
Does a monitoring relay interrupt the main power circuit?
No. Its output contact is a signal-level SPDT or DPDT contact that drives a contactor coil, a PLC input, or an alarm — it is not rated to switch motor or feeder current directly.
What is the difference between a monitoring relay and a protective relay?
Both fall under IEC 60255, but a protective relay is built to the protection-class requirements for interrupting fault current paths on feeders and motors with coordinated time-current curves, while a monitoring relay watches a single quantity against an adjustable threshold and switches a low-power output. A PLC can replicate some monitoring functions in software, but loses the hard-wired, power-independent response of a dedicated relay.
Why does my monitoring relay need a separate auxiliary supply?
Most single-function voltage, current, level, and temperature monitors need a control-voltage feed (commonly 24V DC or 230V AC) to power their internal electronics. Three-phase supply and phase-sequence monitors are the main exception — many draw operating power directly from the measured lines.
What does hysteresis do on a monitoring relay?
Hysteresis sets the gap between the trip value and the reset value. Without it, a reading sitting right at the threshold makes the output relay chatter on and off; with hysteresis set correctly, the output stays in one state until the quantity clearly recovers past the reset band.
Should I choose automatic or manual reset?
Manual (latched) reset for faults where an unattended restart could damage equipment or create a hazard — a dry-running pump or an unmanned line after a phase-loss trip. Automatic reset where nuisance downtime is the bigger concern and the fault condition is self-clearing, such as a brief voltage transient.
Can one monitoring relay cover both voltage and current?
Some multifunction models do — Schneider's RM35TF and similar higher-end ranges combine several quantities in one 22.5-45 mm housing. Single-function relays remain more common where panel space and simplicity are not competing constraints.
监测继电器主要执行一项核心任务：测量某项参数，将其与带有迟滞（hysteresis）特性的阈值进行比较，并在动作延时结束后切换输出状态。至于具体监测哪种参数、采用故障安全（fail-safe）模式与否，以及选择自动复位还是锁定复位，这些都属于规格选型范畴，而非设备本身的局限性。只要根据实际的电源和负载情况（而非仅仅沿用出厂默认设置）来设定阈值、迟滞和延时参数，现场绝大多数因误动作引发的投诉问题便能迎刃而解。
A monitoring relay does one job well: measure a quantity, compare it to a threshold with hysteresis, and switch an output after the trip delay has run. Everything else — which quantity, fail-safe or not, auto or latched reset — is a specification decision, not a limitation of the device. Get threshold, hysteresis, and delay set to the actual supply and load, not the factory default, and most of the nuisance-trip complaints in the field disappear.
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