Editing Hold Modules

Hold modules belong to the Advanced Process template (if you cannot find this template you may need to attach it). After you have added a Hold module by dragging it onto the flowchart view, you can edit it by double clicking. You can change the Name of course, but the main functionality is determined by the Type. There are 3 types of Hold module and we will discuss each one of them separately.

Wait for Signal

This Hold module stores entities in a queue until a unique signal is recieved during the simulation. Each time the signal is received a specified number of entities (defined by Limit) will leave the Hold module queue.

Consider the example of simulating cars queing at a parking building exit while waiting for their prepaid parking tickets to be approved. The cars ( entities) must wait for the signal 10 to be sent in the simulation. When this signal is sent, one car (as defined by Limit) will proceed through the exit.

Scan for Condition

This Hold module stores entities in a queue until a condition is satisfied. However, the Hold module ONLY checks this condition WHEN A CALENDAR EVENT OCCURS. If the condition is true then the first entity in the queue may leave the Hold module. This generates a new event and the condition is checked again. Each time the condition is true an entity leaves the Hold module queue.

Below is an example of a Scan for Condition Hold module from the case study: Courier Service Model. As long as LoadingInnerCity is equal to one entities will leave the Hold module.

Infinite Hold

This Hold module stores entities in a queue for an infinite duration while the simulation is running.

NB: An infinite hold is usually combined with a Search module and a Remove module (See Arena help for more details).

Consider the example of simulating an emergency waiting room. Incoming patients (entities) are placed into a queue based on their Patient Type. Patient Type is an attribute assigned to each entity earlier in the model. Patients will wait in the Emergency Room Hold module in queue until they are removed from the queue by an nurse (entity) at a Remove module.

-- MichaelOSullivan - 25 Aug 2009