Simrad fluid level sensor

mrfishcado

Los Panchos Sportfishing
Mar 25, 2006
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1996 Ranger 488VS 1980 24' Skipjack "La Cuarentona"
I have a Simrad fluid level sensor and it is not working. I have it hooked up to my fuel tank sending unit. Without the sensor installed the ohm readings on the sending unit are fine. As soon as I hook up the sensor it shoots the ohm readings up. Has anyone experienced this before?
 
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a7ewizard

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WARREN WEISENBURG
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First of all, the Simrad sensor can only be connected to the nmea 2000 network. You can not connect it and also have the older analog fuel gage also hooked up.

It also needs to be calibrated by using a Simrad/Navinco based MFD or display ( Suzuki C10 engine display works in this regard).
 
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mrfishcado

Los Panchos Sportfishing
Mar 25, 2006
615
299
Pomona, CA
Name
Paco
Boat
1996 Ranger 488VS 1980 24' Skipjack "La Cuarentona"
There is also a NMEA 2000 part specific to SIMRAD you need. I can look for the one we have and get back to you if that’s helpful
Yes if you don’t mind. There is nothing hooked up to the sender and it is hooked up to a NSS7 via NMEA 2000.
 

ShadowX

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I have a Simrad fluid level sensor and it is not working. I have it hooked up to my fuel tank sending unit. Without the sensor installed the ohm readings on the sending unit are fine. As soon as I hook up the sensor it shoots the ohm readings up. Has anyone experienced this before?

Is this the sensor you have?
1616225862636.png

Before jumping into conclusions and go straight for calibration, you need to verify all the various sensors and sending units are working properly.

First step is to verify the sensor is configured properly and working correctly. Make sure your fish finder is set to use the correct device first.
1616227008207.png



Per the instructions, the Simrad sensor is designed to operate with a standard 33.5 to 240 ohm fluid level sending unit. If you have variable potentiometer in that range, you can connect to test it out. If you don't, just put in a fixed resistor value of around 50 ohms and 240 ohms to test if the readings show up properly on your fish finder. You can find resistors very easily or ask someone who knows about electronics. If you don't have resistors, you can skip to next step, but you won't know for sure if the sensor is working properly within the high and low range without testing.

Once you verify that its sending properly, you can use an ohmmeter to test out the resistance on your fluid level sending unit on the fuel tank to make sure its in the 33.5 to 240 ohm range. Use all precaution in this step. Make sure you ground yourself to get rid of static charge first to prevent static shock/sparks. If you get a reading that a lot higher or lower, the fluid sender on the tank is faulty, the fluid sender is not compatible, or the wires and/or connections are bad.

If you get high resistance readings, another thing to check is for corrosion. Salt water may have gotten into the wiring or connections and cause the resistance to be much higher. Its very common to have corrosion inside the wires or on the terminals that connect to the sending unit. Best way is to test the resistance of the wires at connection point to the sending unit to the Simrad sensor and then repeat the same test at the sending unit terminals mounted to the tank (wire resistance isolated and not included). Make sure in this test, you disconnect the wires to the Simrad sensor and leave the two wires end open and not touching each other. If you have to, tape the wire end with electrical tape to make sure its not touching. If there are major differences between the two measurements, that difference in resistance is all due to the bad wires or bad electrical connections.

Most of the time, you will find out its just a bad wire with corrosion that caused the resistance reading to be high. If that is the case, the best way is to run new marine quality wires to the sending unit. If you can't do that, look for corrosion near the terminals first. If you see green color or white salt residue, its a sure sign that corrosion got into the wire. Cut the connectors off and strip the wires. If the wires are black, you need to cut more wires until you get clean copper or tinned wires. Once you have clean wires, you can twist the two wires together first. Go back to the other end near the sensor and measure resistance. If the resistance is still high, you need to trim more or clean the wires with some sandpaper. If the resistance is low and the wires look clean, terminate the ends with a shrink sleeve terminal to prevent water intrusion. I would personally run new wires, but I know its not always easy or feasible. The wire is damaged and it may fail again in the future. When water gets in between the strands of wires, it tends to wick up even a few feet from the ends. Another way for it to corrode is when the insulation is broken and water gets in through that broken insulation.


1616226180488.png


At this point, you already know if you sending unit is at the correct resistance range. The resistor test on the NMEA 2000 sensor already proved that it shows different fluid level using a lower and higher resistor value.

If the measurements on the sending unit looks fine and the resistor test looks good, the only thing left is software and calibration. You can do a quick 2 point calibration before you refuel on next trip. You can also do a 3 or 5 point calibration also.



1616227478009.png
 
Last edited:

mrfishcado

Los Panchos Sportfishing
Mar 25, 2006
615
299
Pomona, CA
Name
Paco
Boat
1996 Ranger 488VS 1980 24' Skipjack "La Cuarentona"
Is this the sensor you have?
View attachment 1265435
Before jumping into conclusions and go straight for calibration, you need to verify all the various sensors and sending units are working properly.

First step is to verify the sensor is configured properly and working correctly. Make sure your fish finder is set to use the correct device first.
View attachment 1265438


Per the instructions, the Simrad sensor is designed to operate with a standard 33.5 to 240 ohm fluid level sending unit. If you have variable potentiometer in that range, you can connect to test it out. If you don't, just put in a fixed resistor value of around 50 ohms and 240 ohms to test if the readings show up properly on your fish finder. You can find resistors very easily or ask someone who knows about electronics. If you don't have resistors, you can skip to next step, but you won't know for sure if the sensor is working properly within the high and low range without testing.

Once you verify that its sending properly, you can use an ohmmeter to test out the resistance on your fluid level sending unit on the fuel tank to make sure its in the 33.5 to 240 ohm range. Use all precaution in this step. Make sure you ground yourself to get rid of static charge first to prevent static shock/sparks. If you get a reading that a lot higher or lower, the fluid sender on the tank is faulty, the fluid sender is not compatible, or the wires and/or connections are bad.

If you get high resistance readings, another thing to check is for corrosion. Salt water may have gotten into the wiring or connections and cause the resistance to be much higher. Its very common to have corrosion inside the wires or on the terminals that connect to the sending unit. Best way is to test the resistance of the wires at connection point to the sending unit to the Simrad sensor and then repeat the same test at the sending unit terminals mounted to the tank (wire resistance isolated and not included). Make sure in this test, you disconnect the wires to the Simrad sensor and leave the two wires end open and not touching each other. If you have to, tape the wire end with electrical tape to make sure its not touching. If there are major differences between the two measurements, that difference in resistance is all due to the bad wires or bad electrical connections.

Most of the time, you will find out its just a bad wire with corrosion that caused the resistance reading to be high. If that is the case, the best way is to run new marine quality wires to the sending unit. If you can't do that, look for corrosion near the terminals first. If you see green color or white salt residue, its a sure sign that corrosion got into the wire. Cut the connectors off and strip the wires. If the wires are black, you need to cut more wires until you get clean copper or tinned wires. Once you have clean wires, you can twist the two wires together first. Go back to the other end near the sensor and measure resistance. If the resistance is still high, you need to trim more or clean the wires with some sandpaper. If the resistance is low and the wires look clean, terminate the ends with a shrink sleeve terminal to prevent water intrusion. I would personally run new wires, but I know its not always easy or feasible. The wire is damaged and it may fail again in the future. When water gets in between the strands of wires, it tends to wick up even a few feet from the ends. Another way for it to corrode is when the insulation is broken and water gets in through that broken insulation.


View attachment 1265437

At this point, you already know if you sending unit is at the correct resistance range. The resistor test on the NMEA 2000 sensor already proved that it shows different fluid level using a lower and higher resistor value.

If the measurements on the sending unit looks fine and the resistor test looks good, the only thing left is software and calibration. You can do a quick 2 point calibration before you refuel on next trip. You can also do a 3 or 5 point calibration also.



View attachment 1265440
Thanks for all the info. That is the sensor I have. I did the ohm test on the sending unit and I do get 33-240 ohms. When I wire the Simrad sensor to the sending unit the resistance goes way up. With the sensor wired and the sending unit out of the tank I can move the float level up and down but the screen doesn’t change. I spoke to Simrad and they said it was a faulty sensor so they are sending me a new one.
 

ShadowX

I Should Upgrade My Account
Oct 10, 2010
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Thanks for all the info. That is the sensor I have. I did the ohm test on the sending unit and I do get 33-240 ohms. When I wire the Simrad sensor to the sending unit the resistance goes way up. With the sensor wired and the sending unit out of the tank I can move the float level up and down but the screen doesn’t change. I spoke to Simrad and they said it was a faulty sensor so they are sending me a new one.

That definitely sounds like a bad sensor. You should see the level change if you go from the 33 ohm to 240 ohm range. The calibration process is really there to fine tune the reading so it matches the exact amount of fuel in your tank.

When you say the resistance goes way up, are you reading it on the fish finder screen or measuring it with an ohmmeter while its connected to the sensor? Sometimes if you use the ohmmeter to probe the connection with it connected to the sensor, you get false readings because in ohmmeter mode, it sends a small voltage into the circuit to detect the resistance. With it wired to electronics, there could be a negative or positive voltage that gives the wrong results. Sometimes the current is enough to blow the sensor if the sensor circuit is not protected properly against the voltage and current from your ohmmeter. Most sensors have an analog to digital circuit to convert the reading to a digital value. They also put in a pull-up or pull-down resistor to the input connection. That will definitely give you false readings on your ohmmeter if you connect to them.
 

mrfishcado

Los Panchos Sportfishing
Mar 25, 2006
615
299
Pomona, CA
Name
Paco
Boat
1996 Ranger 488VS 1980 24' Skipjack "La Cuarentona"
That definitely sounds like a bad sensor. You should see the level change if you go from the 33 ohm to 240 ohm range. The calibration process is really there to fine tune the reading so it matches the exact amount of fuel in your tank.

When you say the resistance goes way up, are you reading it on the fish finder screen or measuring it with an ohmmeter while its connected to the sensor? Sometimes if you use the ohmmeter to probe the connection with it connected to the sensor, you get false readings because in ohmmeter mode, it sends a small voltage into the circuit to detect the resistance. With it wired to electronics, there could be a negative or positive voltage that gives the wrong results. Sometimes the current is enough to blow the sensor if the sensor circuit is not protected properly against the voltage and current from your ohmmeter. Most sensors have an analog to digital circuit to convert the reading to a digital value. They also put in a pull-up or pull-down resistor to the input connection. That will definitely give you false readings on your ohmmeter if you connect to them.
Thanks for all your help. Once I get the replacement I’ll let you know if that solved the issue.