Begin with an explicit switching rule
A 控制器 needs both a value and a rule for changing state. VEGA's VEGAMET 391 instructions distinguish filling and emptying pump duties and warn against identical switching points. Consult the selected 控制器's actual manual; its relay modes and electrical contact states must not be inferred from a generic sketch.
For an emptying duty, a typical two-threshold rule is to start at the upper 液位 and stop at the lower 液位. Between these 液位s, retain the preceding operating state. Filling reverses the process demand: start at the lower threshold and stop at the upper. Define whether a command is based on 液位 height, percentage or volume. A percentage of height is not automatically the same percentage of volume in every tank shape.
Hysteresis is a band; a delay is a separate condition
With height-based thresholds, the band is the upper 液位 minus the lower 液位. It reduces repeated switching close to a single threshold. A start delay or a minimum run time addresses a different requirement; it does not redefine the two 液位s. Document each separately, including which protective condition may override a time constraint.
Choose the band with the usable storage, changing in流量, pump capacity and the motor or drive manufacturer's start/stop restrictions. There is no universal recommended percentage in this guide. Surface movement, 传感器 filtering and 控制器 timing must also be considered when the project owner defines the control schedule.
A calculation example with stated assumptions
Consider a hypothetical straight-sided basin with constant horizontal area A = 10 m². An emptying pump starts at 2.4 m and stops at 1.8 m above the same datum. Assume in流量 remains 2 m³/min and the running pump removes 8 m³/min throughout the band. Ignore startup transients, delay and changing pump performance for this arithmetic example.
- Hysteresis: 2.4 − 1.8 = 0.6 m.
- Working volume between thresholds: 10 × 0.6 = 6 m³.
- Net emptying rate while running: 8 − 2 = 6 m³/min; run time is 6 ÷ 6 = 1 minute.
- Refill time while stopped: 6 ÷ 2 = 3 minutes.
- Idealized cycle: 4 minutes, equivalent to 15 starts per hour.
These are teaching values, not WESIVO specifications or recommended settings. Compare an actual duty against the pump and motor limits and recalculate for its geometry and varying 流量s. If pump 流量 does not exceed in流量, this emptying calculation cannot produce a finite drawdown time.
Define measurement faults and pump faults separately
The FlexView FMA90 para仪表 manual treats pump failure behavior as a configurable function. This supports a practical review question, not a universal instruction to keep a pump running or to stop it: what action has the site designer approved for each failure?
An invalid 液位 input is not evidence that the basin is empty. A last displayed value is not proof of a current valid measurement. Record 传感器 fault, loss of communication where applicable, commanded state, running feedback and pump fault as distinct conditions. Agree on alarms, automatic restart and manual intervention with the responsible control engineer. Determine any independent protective functions from the project risk assessment.
Commission against a sequence table
Record the initial state, rising and falling 液位, exact threshold crossing, expected command and actual feedback. Test the state retained inside the band, and separately test any approved timing, signal-fault and power-recovery behavior. An electrical simulation verifies logic at its injection point, not 传感器 installation or actual pumping performance.
WESIVO SL09A and WSRD-08WA links below are measurement-选型 routes in the confirmed 液位 catalogue. Confirm the actual output and 控制器 input compatibility. The example does not assign relay logic, safety certification, pump control or a guaranteed response time to these 仪表.
先写清楚切换规则
控制器不仅需要测量值，还需要改变状态的规则。VEGA 的 VEGAMET 391 说明书区分补水与排水泵工况，并提醒不要将启停点设为同一值。应核对所选控制器的实际说明书，不能根据通用示意图推定继电器模式和电气触点状态。
排水工况常见的双门限规则是：液位达到上限时启动，下降到下限时停止；处于两者之间时，维持先前运行状态。补水则相反：下限启动、上限停止。还应明确指令基于液位高度、百分比还是体积。不同池体形状下，高度百分比不一定等于体积百分比。
回差是一段区间，延时是另一项条件
采用高度门限时，回差带为上限液位减去下限液位，可减少单一门限附近的反复切换。启动延时或最短运行时间处理的是另一类要求，不会重新定义两个液位。应分别记录，并说明哪些保护条件允许覆盖时间约束。
回差带应结合可用蓄水量、进水变化、泵能力以及电机或驱动器制造商规定的启停限制确定。本文不推荐通用百分比。项目责任方制定控制表时，还应考虑液面波动、传感器滤波及控制器时序。
带明确假设的计算示例
假设一座直壁池的水平截面积恒为 A = 10 m²，排水泵在同一基准以上 2.4 m 启动、1.8 m 停止。假设整个区间内进水保持 2 m³/min，泵运行排水保持 8 m³/min。这里只演示算术，忽略启动瞬态、延时及泵性能变化。
- 液位回差：2.4 − 1.8 = 0.6 m。
- 两门限之间的工作容积：10 × 0.6 = 6 m³。
- 运行时净排水量：8 − 2 = 6 m³/min；运行时间为 6 ÷ 6 = 1 分钟。
- 停泵后的补水时间：6 ÷ 2 = 3 分钟。
- 理想循环为 4 分钟，折合每小时启动 15 次。
以上是教学数值，不是 WESIVO 参数或推荐设置。真实工况须对照泵和电机限制，并按实际池体与流量变化重新计算。若泵流量不大于进水量，这个排水公式无法给出有限的降液位时间。
分别定义测量故障和水泵故障
FlexView FMA90 参数说明书将泵故障行为列为可配置功能。由此应提出的审核问题是：现场设计人员对每种故障批准了什么动作；不能将其理解为所有工况都应继续运行或都应停泵。
液位输入失效不等于池内无水。屏幕保留的上次数值也不能证明当前测量有效。应分别记录传感器故障、适用时的通信中断、泵指令、运行反馈与泵故障，并由控制责任工程师约定报警、自动重启及人工干预方式。是否需要独立保护功能，应由项目风险评估确定。
按顺序表调试
记录初始状态、液位上升与下降、门限越过时刻、预期指令及实际反馈。核对区间内的保持状态，再分别测试已批准的延时、信号故障与恢复供电行为。电气模拟只验证注入点之后的逻辑，不验证传感器安装或真实抽水能力。
下方 WESIVO SL09A 与 WSRD-08WA 是已确认液位样册中的测量选型入口，应核对实际输出与控制器输入的兼容性。本例不为这些仪表赋予继电器逻辑、安全认证、泵控能力或保证响应时间。
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