假设您有四个可用的泵，并且您不会一次运行所有泵。当是时候开始一个，您想选择磨损最少的一个。

您可以通过比较每个泵运行的总时间来决定要开始哪一个。对于总体来说，这是一项工作。

这是关于使用Opto 22总计的两个关键问题SNAP PAC System：

• First, both analog and digital totalizers arebuilt-in featuresin SNAP PAC I/O processors (brains and rack-mounted controllers). So there's no need to buy one.
• Second,totalizer commands被内置在PAC控制中，因此您可以轻松地在SNAP PAC控制器上运行的控制策略中使用它们。

那么我们如何开始呢？我们首先将四个泵接线到4点快照数字输入模块，例如snap-iac5。（我们选择一个4点模块，而不是高密度数字模块，因此可用的总体功能。）

When we configure the four points in PAC Control, we make sure to choose Totalizer as a point feature. Once the feature is configured, the brain automatically begins tracking the total amount of time the point is on and the total amount of time the point is off. These values continue to increase for 4.97 days, at which point they roll over and start again at zero.

Now on to our control strategy. In this application we're interested in how long the pumps have been on, so the commands Get On-Time Totalizer and Get & Restart On-Time Totalizer are the ones to look at. (There are also commands for off-time totalizers, which could help indicate down-time. But that's another issue.)

命令详细信息Command Help orPAC控制命令参考向我们展示大脑返回控制器一个代表的浮子秒，分辨率为100微秒。对于我们的泵应用that maximum duration of 4.97 days might be a problem.

So we'll use Get & Restart On-Time Totalizer to read the totalized values for each pump every minute and reset them to zero. Then for each point we add the new value we just read to a variable that holds the cumulative total. These variables we keep in a float table, and we make the table persistent so the values can't be lost, even if power to the controller is lost.

Once we compare these totalized values for each pump, we can determine which one to start.

A最近的OptoForum帖子提供一些示例代码帮助您在自己的策略中构建这种逻辑。看看，并将自己的改进添加到论坛上。