INTRODUCTION
A level sender is a sensor that is installed into a tank to measure the level of fluid.
The terms sender and sensor are used interchangeably to describe the same thing: a device that senses the level, temperature or pressure, then sends it to a gauge or digital display.
As Wema fuel level sensors are made of stainless steel, with a NBR float, they can be installed in most viscous solutions; petrol, water, oil, fertiliser, whisky... if in doubt, just ask and we can advise if it is suitable for your application.
Wema senders are also double insulated so the internal electronics are isolated from the body of the sender and the contents of the tank. This not only adds protection for the electronics, it is also far safer than other brands of senders that can allow current to enter the tank. Never a good idea to mix fuel with stray electric current!
INSTALLATION
The sender is either bolted down to the top of tank, screwed into a boss or flange or, in the case of larger truck senders like the TX range, are secured with a bayonet fit. Flanges are either made of stainless steel or plastic. Stainless steel provides excellent strength and corrosion resistance and nylon plastic flanges are particularly useful for aluminium tanks to prevent galvanic corrosion. It is also possible to install an inspection hatch into the top of the tank with a 1.25" BSP thread incorporated into it, allowing you to install a sender without cutting more than one hole. If you are retrofitting a Wema sender and the old one had a different fitting, you may require a converter to adapt the hole. We manufacture a wide range of different converters made from nylon, brass or stainless steel.
The wiring is very simple. Resistance senders have two wires. One wire (it doesn't matter which one) is connected to battery negative and the other is connected to the signal wire on the gauge or display.
The sender is passive, so only a few milliamps of current is provided by the gauge to give a reading. It is important to note that you should never connect a resistance sender directly to 12v as this will burn out the internal components.
For 0-10 or 0-5 volt senders, these will have there wires; positive, negative and signal. It is very important not to connect these senders incorrectly as putting the positive feed to any other wire can damage the sender.
OUTPUT
Level senders are available with various different outputs, the most common being resistance, 0-5v, 0-10v and 4-20mA. For connecting to a traditional analogue gauge, resistance senders are used. Voltage senders are usually only used for connecting to digital systems and displays.
The majority of resistance senders are manufactured in two different resistance ranges, commonly referred to as European and American specification. European specification is 0-190ohms and American specification is 240-30ohms.
The resistance ranges have become know as American and European purely due to the fact that, historically, the 240-30ohms resistance range was used more by US boat builders and 0-190ohms was favoured by European Original Equipment Manufacturers (OEMs) – rather like 240v/110v AC, PAL/NTSC etc. Today, both resistance ranges are used on both sides of the Atlantic and all over the world.
There is no advantage or disadvantage to either resistance range but it is important that your sender and gauge both operate on the same range otherwise they won't work together. An obvious sign that you have a mismatched sender and gauge is that the gauge will work backwards.
Generally a sender with two wires is a resistance sender and one with three wires is a voltage output sensor. There are exceptions, however: sometimes we make resistance senders with high or low level alarms and these can have three, four or five wires. Normally the output of the sender is stamped onto the ID plate on the top, above the wire.
Dedicated digital output senders are also available, either for NMEA2000, a marine based communication protocol or CAN BUS J1939, a similar protocol for other land-based vehicle management systems.
Wema senders work with magnetic reed switches, situated on the Printed Circuit Board (PCB) inside the sender body. Inside the float are a pair of magnets that trigger these switches as the float moves with the fluid in the tank. As the float is independent there are no moving parts to wear out or break. This is one of critical differences between Wema senders and others on the market – we regularly see Wema senders and gauges still in use 25 years or more after they left the factory.
RESOLUTION
Over the last 40 years, Wema has been continually developing and innovating new technology and a modern sender now has far more switches packed in much tighter together to give a better resolution display of what's in the tank.
As a general rule, a standard resolution sender has a switching point every 20mm and a high resolution sender changes state every 10mm.
The shorter the sender is, the more important the resolution becomes as the percentage of a shallow tank is a much smaller distance of movement for the float than on a very large tank. For instance; in a 400mm deep tank 10mm of movement represents 2.5% of the fluid in the tank whereas in a tank that is 1500mm deep 10mm of movement only represents 0.6%. This is why our high resolution range is concentrated on the shorter senders. It is possible to manufacture longer senders at higher resolutions when the customer has a specific need.
WHY WEMA?
So what is the difference between a Wema level sender and another sender that looks the same but is a fraction of the price?
It all comes down to quality. Quality of the internal components and the level of quality control and testing.
40 years of knowledge and innovation and, of course, the standard of support that we offer all of our customers.
Most Wema products are sold with a 3-year guarantee because we are confident that our products will stand up to the harshest environments and keep you informed and protected for years.
Remember, it's easy to make a cheap copy of a product if you don't support or guarantee it.