RADAR

Radar level sensors are optional on asphalt tanks and serve the same purpose as optional gauge boards (Fig. 12). Most HMA plants use one or the other. The antenna on a radar unit requires cleaning periodically (Fig. 13). Vapors from the liquid asphalt tend to leave thin deposits on the antenna over a period of time. These deposits can build up and decrease the sensitivity of the radar. Consequently, the radar may not provide accurate indications of asphalt level in the tank.

Figure 12. Vega radar sensor unit.

Figure 13. Antenna of radar unit needs to be cleaned regularly to ensure reliable level indications. Unit should be removed from tank for access to clean the antenna.

To clean the antenna, simply unbolt the radar unit from the top of the tank and pull the unit out of the tank with wires attached. But before pulling the unit out, take special note of the position of the small hole drilled in the side of the radar body. This hole should face towards the center of the tank and is the position it was in when the unit was calibrated. Clean the antenna with a rag soaked with solvent and reinstall the unit. Make sure that the drilled hole faces the exact same way it was before the unit was removed. Otherwise, the unit will not work properly.

Cleaning the antenna once a month during the operating season should be adequate. However, any time you encounter false level indications, the first thing to do is to clean the antenna. Your experience may indicate that it needs cleaning more often than once a month.

Aside from keeping the antenna clean, your radar unit should not require any other routine maintenance. However, if you ever need to replace the radar unit with a new one and the new one has not been set up for your specific tank, you will need to do that. Please refer to Heatec Tec-Note applicable to setting up your radar unit.

RADAR SHUTOFF CONTROLS

When the tank is being filled, the radar senses when the asphalt reaches a preset “full” level. Consequently, it causes the unloading pump to shut off.

The radar also senses when the asphalt has reached a preset “empty” level. The radar reacts to the preset empty level by closing the temperature control valve that supplies hot oil to the tank coils. This prevents coking the coils.

If asphalt residues have coated the antenna of the radar unit, the radar unit may fail to shut off the unloading pump when the tank is full. Or it may fail to shut off the hot oil when the tank is empty. The remedy is to clean the antenna as described previously.

If cleaning the antenna does not remedy the problem, the radar unit may not be properly programmed. Please refer to the Heatec Tec-Note applicable to setting up your radar unit.

You can check both of these functions controlled by the radar by temporarily changing its Honeywell controller (Fig. 14) as described below. The applicable Heatec Tec-Note previously listed provides information for setting Honeywell controllers used with Heatec vertical asphalt tanks.

Figure 14. Honeywell controller used with radar unit.

It is helpful to use two people to check both radar shutoff functions. When checking for proper high level control, one person should be at the Honeywell controller. The other person should be at the controls of the asphalt unloading switch (Fig. 15). Make sure the pump controls are set for the tank you are testing. Also make sure that the tank fill valve is open.

Figure 15. Controls for unloading pump.

Take note of the actual asphalt level indicated by the Honeywell controller. If the tank is less than full, momentarily turn on the unloading pump. The pump should operate. Then reset ALARM A2S1VA on the Honeywell controller to a value for any level below the actual level. Turn on the unloading pump again. It should not operate. Moreover, this should set off an alarm horn and cause a red light to come on at the controls of the unloading pump. Reset all controls to their normal condition.

When checking for proper low level control, one person should be at the Honeywell controller (Fig. 14). The other person should be at the power-actuated temperature control valve on the side of the tank (Fig. 3 and 4).

Take note of the actual asphalt level indicated by the controller. Reset the UL temperature controller to a set point higher than the current temperature of the asphalt and make sure the power-operated hot oil valve is diverting hot oil so as to heat the tank coils. Then reset ALARM A1S1VA on the Honeywell controller to a value for any level above the actual level. The power-actuated valve should rotate so as to bypass the hot oil, thereby shutting off heat to the tank.

Reset all controls to their normal condition.

NOTE: In normal operation the radar shuts off the unloading pump before the proximity switch is activated. Thus, if the proximity switch shuts off the unloading pump it means that the radar is not working properly.

So every time you fill the tank pay special attention to whether the indicator light for high float level comes on. If it does come on, this indicates that the radar failed to shutoff the unloading pump and the shutoff was achieved only by the backup system.