Tank Level Sensors
TANK SENSORS ARE KEY TO FAULTLESS MEASUREMENT
|RV Arm||$54||Poor 15-20%||IP68||Poor for Grey/black water|
|Compact External Pressure||$59||V High 2%||IP65|
|Normal External Pressure||$170||V High 2%||IP67||OK for creek crossings|
|Submersible||$280||V High 2%||IP68||Feed through Breather|
|Ultrasonic||$99||High 2-4%||IP68||Fits under tank|
|Wema Top Mounted||$85||Mod 5-10%||IP67||Fits on top of tank|
Problems faced by users measuring water tank levels start with the sensors:
The caravan Industry "cheap" sensor is known as "RV Arm". A typical example is shown on the right.
It has 5 sensor points that are fixed in position on the plastic arm.
This means that the "accuracy" of the tank measuring can be as much as 19% out. If the tank is not perfectly square (and they never are), then this "linear sensor" accuracy gets worse.
Plus these are expensive at $54.94 shown in the on-line store. They are only plastic after all.
The accurate alternative can measure your tank volume within 2% accurarcy.
PRESSURE BASED LEVEL SENSORS
These sensors use "differential pressure" to measure the height of liquid in your tank. They work equally as well on grey water or black water as fresh water. The stanless steel sensor has a "mems" disc that accurately measures the differentail pressure. The IP 67 and IP 68 sensors have a small tube in the cable that "measues the atmospheric pressure" as a differential to the tank + atmospheric pressure. In so doing, no matter what the altitude nor barometric pressure, the tank level measure will be accurate.
There are 3 different grades of level sensors:
- IP 65 is compact and in-expensive. Its good fot washing and fast creek crossing but not suitable if your park in the middle of the creek for a break!
- IP67 is small and reasonable price. Its good for parking in the creek for less than 30 mins and less than 1m deep.
- IP68 can be parked in the creek all year!
Now you have sensors for accurate tank measurement!
ULTRASONIC BASED LEVEL SENSORS
These are so easy to use and quite different to the "top of tank" air based sensors.
These bond to the underside of the tank. They work with any tank that has no paint not possible air layer between the sensor body and the tank. They are perfect with metal and "roto moulded" plstic tanks.
Q: My tank has a taper at one end and is not square, what is the effect on accuracy?
A: Not much effect on accuracy: We calibrate the tank into segments, up to 10. This means that as the shape changes with level height, we can assess the volume quite accurately between each segment. So the absolute accuracy will be the difference in the linear measurement and volume in a 10% increment. Practically this is a very small variation.
Q: How do I fit these pressure sensors?
A: Typically, these are fitted to either the drain bung or the bottom of tank tap assembly. Alternatively, you can drill and tap for new fittings as well. It is best to do this near the edge of the tank where there is greater thickness. The drain bung option is usually drilling and taping a BSP 3/4inch bung with the sensor. Very easy to do.
Q: I have the RV srm type of sensors and want to keep these as it is easy on the instal!
A: No problem, we have an interface that will read 3 of these sensors and translate the signal into the voltage need for our system.