Worth Data 7000 manual How Relay Stations work…, Relay n Cannot be

Relay Stations

Since the range of the LT7001 Terminal is quite large you probably won't need a relay unless you must have coverage in more than one location that is difficult to cover with a single base. An example of this would be inside two or more metal buildings where a base would be in one building and a relay in the other. Relays work like a remote antenna, passing data to the Base Station via cable instead of radio frequency. Base Stations are used as Relay Stations by changing the jumpers inside. See Appendix A for details.

Relay Stations are attached to the Base Station using a cable that connects from the Base’s RELAY port to the Relays’ RELAY port. When you order a Relay Station, you receive a 3-foot test cable with it. Although Relay Stations will increase your range of operation, they will also add about ½ second to the response time.

How Relay Stations work…

It helps to know how Relay Stations work before you add them to your system. Although Relays increase your operational range, they also slow the response time of your system. In order to use Relays, the Terminal must be configured to acknowledge that Relays are present. This is done using the Relay Existence setup parameter. By default, the RF Terminal is not configured to look for Relays. See Chapter 2; RF System Setup for details.

Once the RF Terminal is Relay-ready, it can use the Relay instead of the Base Station to communicate. If a RF Terminal tries to transmit 10 times to a Base Station without a response, it broadcasts a “who can hear me” message. If both the Base Station and the Relay hear the message, whoever answers back to the RF Terminal first becomes the point of contact for that RF Terminal.

Once a RF Terminal has established communication with a Relay, it addresses that particular Relay until another communication failure (10 transmissions with no response) occurs. If a Base Station is within hearing distance of the RF Terminal, it will ignore messages meant for the Relay.

When a Relay receives data from a RF Terminal, it then transmits that data to the Base Station over RS-422 twisted-pair cable. The Base Station in turn transmits data (via cable) for that RF Terminal to the Relay, for subsequent broadcast to the RF Terminal.

Relays are “dumb”. Relays do not know whether a transmission was received by the Base Station or not, so it is up to the RF Terminal to retransmit its data if it does not receive a message from the Host Computer (via the Relay). The Relay can recognize data from the Terminal though and if it receives 10 retransmissions from the RF Terminal, the Relay assumes that the Base Station cannot hear it and broadcasts the message:

RELAY n CANNOT BE

HEARD BY THE BASE

NOTIFY SUPERVISOR

PRESS ANY KEY