时序与定时例程 6：一用一备轮换（每次启动换一台）

这一页只讲这一个例程。母页 b-02-timing 里留着例程 1，其余例程各自一页、在那一页的目录里点。

场景：两台泵/风机，平时只开一台，每次启动换另一台让磨损均匀；当前这台故障就自动落到另一台。

软元件

软元件	作用
X0 / X1	开泵 / 停泵请求
M60	运行需求
D610	轮换标志（0 = 1 号，1 = 2 号）
M61 / M62	1 号 / 2 号故障
Y0 / Y1	1 号泵 / 2 号泵

块图（照着拖即可）

对应的 ddc.json（点「生成 JSON」得到的就是它；也可存成 .ddc.json 导入）

{
  "version": 1,
  "name": "一用一备轮换",
  "scan_ms": 200,
  "lines": [
    {
      "op": "assign",
      "target": {"op":"ref","device":"M","addr":60},
      "expr": {
        "op": "rs",
        "id": "rs_run",
        "args": [{"op":"ref","device":"X","addr":0},{"op":"ref","device":"X","addr":1}]
      }
    },
    {
      "op": "if",
      "cond": {"op":"edge","edge":"rise","id":"e_rot","args":[{"op":"ref","device":"M","addr":60}]},
      "then": [
        {
          "op": "assign",
          "target": {"op":"ref","device":"D","addr":610},
          "expr": {
            "op": "arith",
            "a": "-",
            "args": [{"op":"const","value":1},{"op":"ref","device":"D","addr":610}]
          }
        }
      ],
      "else": []
    },
    {
      "op": "assign",
      "target": {"op":"ref","device":"Y","addr":0},
      "expr": {
        "op": "and",
        "args": [
          {"op":"ref","device":"M","addr":60},
          {
            "op": "and",
            "args": [
              {
                "op": "cmp",
                "cmp": "==",
                "args": [{"op":"ref","device":"D","addr":610},{"op":"const","value":0}]
              },
              {"op":"not","args":[{"op":"ref","device":"M","addr":61}]}
            ]
          }
        ]
      }
    },
    {
      "op": "assign",
      "target": {"op":"ref","device":"Y","addr":1},
      "expr": {
        "op": "and",
        "args": [
          {"op":"ref","device":"M","addr":60},
          {
            "op": "and",
            "args": [
              {
                "op": "cmp",
                "cmp": "==",
                "args": [{"op":"ref","device":"D","addr":610},{"op":"const","value":1}]
              },
              {"op":"not","args":[{"op":"ref","device":"M","addr":62}]}
            ]
          }
        ]
      }
    }
  ]
}

要点

• 轮换靠 1 - D610 做状态翻转（0↔1），配合「脉冲触发」保证一次启动只翻一次——这就是二分频。
• 故障只做"屏蔽选中"：故障泵不会在这轮被选中，但轮换顺序不变，修好后下次照样轮到它。
• D610 默认 0；必要上电初始化里赋值一次，保证每次下发后都从 1 号开始。

验证：X0 一次 → Y0 = 1；X1 停止后再 X0 → Y1 = 1；把 M61 置 1（1 号故障）后再启动 → Y1 = 1。

注意事项

• 不用「脉冲触发」直接翻转：运行期间每个扫描周期翻一次，两台泵以 200 毫秒的频率来回切。
• 用「或」代替轮换让两台同时启动：那是一用一备变成"双投"，压力/流量会翻倍。
• 故障信号接的是常闭点却当"1 = 故障"用：逻辑反了，故障泵反而被优先选中。