Problem:

How do you test and verify RF communications between an Accutech field unit and a base radio?

Solution:

The RF Channel and RF Baud rate need to match on both the field unit and the base radio.  Let untouched, the display on the base radio will indicate the number of field units reporting back to the base radio ("3 WI"  = 3 Wireless Instruments). But how does one determine the robustness or reliability of the RF signal coming through?

There are two different tests available that can be performed from the field unit:
1 - RSSI - Received Signal Strength Indicator, measures the RF signal intensity as seen at the field unit
2 - LNK TST - Link test that looks at the transmission success rate

1 - RSSI

For firmware 2.03.1 and older, the RSSI Diagnostic, located in the field unit’s diagnostic menu, displays the RF signal strength in one of seven ranges. The signal strength is displayed on the LCD using a combination of ‘>’ and ‘’ characters. Full signal strength is displayed as “> > > > > > >”, while minimum signal strength is displayed as “> _ _ _ _ _ _”. If the field unit is not communicating with the base radio (i.e., NO RF), all underscore symbols will be displayed (“ _ _ _ _ _ _”).

The RSSI is measured every time the field unit receives a message from the base radio. The signal strength of the received message from the base radio is calculated during this time. The actual signal strength in dBm for each range is shown below:


To place the field unit in RSSI Diagnostic mode, start from the DIAGNSE menu, navigate to RSSI and press ENTER.

Now that the field unit is in the RSSI mode, you might try to move the field unit about to see what sort of reception it has, listening for the base radio. Look at the LCD panel; the ‘>’ might fluctuate. One should estimate an average value based on these fluctuations. The ideal signal integrity is seven arrows.

If you see a NO RF message, then satisfactory RF communication is not being made with the base radio. If your application allows, move the field unit to a different position and check again for communications. If your application only allows you to mount at this particular point, you may want to try a slower baud rate setting for an increased range or consider improving the RF path (raising or repositioning the base radio antenna, clearing obstructions from the path, using external antenna at the field unit, etc... )

2 - LNK TST

The Link Test command is located in the field unit’s DIAGNSE menu. Using the <NEXT> and <ENTER> buttons, navigate to link test and press the <ENTER> button to begin the test. The field unit will begin to test the link in both directions (to and from the base radio). During this time, the word TEST will move back and forth across the LCD panel. When the test ends, the field unit displays the quality of the link. Be aware that the field unit uses the configured baud and transmission rates to perform this test. The length of time it takes to perform this test depends on the device’s normal transmitting rate.

The Link Test can be performed from the field unit, the base radio or through Accutech Manager. To place the field unit in Link Test mode, follow the menu map shown below. The Link Test menu is under the DIAGNSE menu and not the CONFIG menu.

When enough messages have been observed by the field unit, the link strength will be shown on the LCD display. A display of 5 STARR indicates the strongest link, while a display of 1 STARR indicates the weakest link. The link test will continue to be evaluated and the rating on the screen may self adjust. Keep in mind that the longer the link test runs, the more data the Field Unit needs to evaluate.

The Link Test reports the percentage of successful messages received from the field unit being tested.

STARR	% Success
5	90-100%
4	80-89%
3	60-79%
2	40-59%
1	0-39%

When performing the field unit installation procedure, be sure to place the field unit in a location where it receives the highest signal strength number possible. A stronger link means fewer data re-transmits and a longer battery life.

Publicerad för:Schneider Electric Sverige