Monitoring old electric power generator instruments

For a monitoring project, I need to read the data from a pair of old Caterpillar Electric Power Generators. This data includes readings from old gauges (like shows in the attached pictures) that measure charge in amperes, battery charge, oil pressure, fuel level. Other data that I need capture comes from some pilot lights that alert if there is conditions light low lube oil pressure, excessive water temperature, overspeed, overcrank, etc. And finally, I need get the position from the rotary switch:

There is another energy generator that display the information in LCD displays like the attached picture:

I know how to deal with arduino sensors, but not with this old instruments. There is a way to “translate” this data in information that Arduino can read?

Do you have the original wiring diagrams?

Does Caterpillar provides a mod-kit ?

A sensor is a sensor is a sensor…
Every sensor has an output
Your onlt tast is to convert the output of the existing sensors into a value that can be read by an arduino.

There is not wiring diagram nor manual available. The generators are too old and Caterpillar doesn’t have Mod Kit for this devices. Maybe I can capture a signal from the pilot lights and send it to the Arduino, but I don’t know how to translate the analog readings from gauges into digital information.

Are these two different generators, one with analog indicators the second one, probably next generation with digital ones?

Obviously the first step would be to measure on the gauges which secondary (translated) value they process. DC or AC? Then measure their indicator range.
Analogue indicators frequently are 100μA-0.1V or 0…10V or 4…20mA ones.
Then the second step would be to measure if they have a bias against GND.

But the most safe approach is probably to leave these electrics as hey are and use your own AC Volt / Ampere /Watt meters transducers.

Welcome to the forum.
It appears that you are asking beginners questions.
But this is not beginners projects.

The best way to do this is to take it one step at a time.

If you could measure only one thing, what would it be?

Once you get that first thing. The rest become much simpler .

Much simpler.

I think the analog meters should be relatively easy to tap into, particularly then ones related to the engine. I’d start at the temperature gauge. There must be 3 wires connected.
V+(which ever voltage is provided, probably 12v DC, since that shows up on the volt meter)
And the wire connected to the sensor. This should provide you with a voltage, since the sensor has an increased resistance with a higher temperature. Problem is though that there will be a lot of noise on the GND an V+ (and on the sensor wire) which the analog dial has no trouble with, but which will cause issues for digital instruments. You will have to filter the signal.
You can lower the volts down to a range suitable for an Arduino by using a voltage divider, but if you want to make sure you don’t influence the reading with any components you add, you should start with putting an Op-Amp, setup as an envelope follower. Just some capacitors might suffice for filtering, but i would first check that with an oscilloscope before you connect an arduino.
Measuring the Frequency (Hertz) i suggest you use an opto-coupler driven by a signal that passes through a rectifier bridge and current-limiting resistors similar to a zero-cross detection if you want to digitally measure it. There are other standard circuits for it, that use the charging and discharging of a capacitor to convert frequency into an analog voltage.
With AC voltage i’d say, first step down with small transformer (coils !) then convert to DC, and measure.

Thank you very much for your answers. The generators works with a pair of 12 volt car battery and there are two different models of this devices. One with analog displays (gauges and light pilots). And the other model works with digital displays.
The first readings that I need “translate” are the measures from analog gauges. I’m waiting to have physical access to the generators to look the wiring schema of this instruments and do some readings.

You seem to indicate these generators are currently in use. You will need a whole lot of access and testing if you are really going to do this project.

Yes, it’s true Paul. It is a great challenge, but I’m worried about that my knowledge is not enough. Even so, I’ll do some tests and the necessary to achieve the project’s objectives. In my country, in the enterprises there is a lot of old equipment like this one and the budgets are very limited, but there is a enormous need of automate a lot of process and devices, so is a very good opportunity to offer a nice solution to low cost.

If I make some progress I would like to share this information with the Community.

That being the case. My first step would be to inventory the various types of equipment and then work on automating the most common type/version.

Thanks Paul is a good advice. On the other hand, I am getting the manuals from a colleague, because the owner of the generators no longer has any information.

What is the EXACT model number from the generator’s data plate?

@JCA34F it is SR4 and the Generator Set is: for the first one 3408 and the second one 3412. I got this manuals from the Web:

Caterpillar Power Generators - Manual

Now I’m reading this information. Also, I’m searching the option for a MODBUS port and if there is one, I can capture the needed information from this port.

PS: sorry for the G Drive links, but Arduino Forum doesn’t admit PDF uploads.

I highly doubt that you will find a digital serial module in an analog generator.
The RS485 might only be on the digital version.

Lots of inputs on the Analog and lots of options to test inputs. all the gauges will be analog so, you can get some practice before you get your hands on the generator.

Pretend I am the owner of the power generating equipment. Can you explain to me how the monitoring you want to do is better/cheaper than me just looking at the instruments on the control panels? Also, as owner, can you tell me if you will modify the machines so they will not be able to operate for some time or perhaps for ever? How much time will you need to modify any one of the machines?
With that information, perhaps you can get better advice from the forum.

perfectly formulated questions :+1:


  1. The owner needs remote monitoring because she/he can’t stand all the time in front of the machine and doesn’t have a way to accomplish this with the actual equipment. On the other hand, her/his budget is very limited to acquire the official Caterpillar solution.
  2. Paul, your questions make me reflect and now I’m thinking in a non-invasive solution with external sensors, like the HC-SR04 for liquid levels, temperature, current meter clamp, and battery charge sensors.
  3. I have 45 days to modify (or complement) the generators.

In any case, this Tuesday I’ll going to take a look at these generators and do some test to start setting up a test laboratory. Thank you very much for these thoughtful questions and approaches.

Maybe just install two webcams?
And I am not even joking!
I looks that a good part of the indicators are mechanical, and at least for the older model, not using DC instrumentation.
Patching so many signal levels and adding sensors where the local indicators are mechanical will not be cheap!

1 Like