DIGITAL INCLINOMETERS FOR RADIO TELESCOPE DISH

Yes – a digital inclinometer can measure the actual vertical inclination/elevation of a radio telescope dish.

Most handheld digital angle gauges contain a MEMS accelerometer which senses gravity.

Typical readings would be:

Dish horizontal          0 degrees
Dish halfway up         45 degrees
Dish vertical/zenith    90 degrees

HANDHELD DIGITAL INCLINOMETERS

A normal magnetic digital angle gauge can simply be attached to a rigid part of the dish which moves in elevation.

Example:

RADIO DISH
    |
    |
    +---- Digital inclinometer
                |
                +---- LCD display
                     37.4 degrees

Advantages:

Cheap
Small
Battery powered
Magnetic mounting often available
Typically 0.1 degree resolution
Directly measures angle relative to gravity

Problem:

Most inexpensive units only display the angle.
They don't provide an electrical output.

HANDHELD UNIT WITH BLUETOOTH

One possibility is:

Wixey WR300BT

Approximate price:

GBP 35-45

Specifications:

Range:          +/-180 degrees
Resolution:       0.1 degree
Accuracy:        +/-0.2 degree
Repeatability:   +/-0.1 degree
Output:          Bluetooth

Therefore:

Dish
  |
  v
Wixey WR300BT
  |
  | Bluetooth
  v
Phone/tablet
  |
  v
Angle displayed remotely

This would be useful if you simply want to see the dish elevation remotely.

BETTER FOR COMPUTER CONTROL

For computer logging or automatic telescope positioning, an industrial electronic inclinometer is preferable.

Possible outputs include:

0-5 V analogue
0.5-4.5 V analogue
4-20 mA
RS-232
TTL serial
RS-485
CAN
Bluetooth

RS-485 OPTION

RS-485 would probably be my preferred solution for a permanent radio telescope installation.

For example:

RADIO DISH
    |
    |
RS-485 INCLINOMETER
    |
    |
    |  Long cable
    |
    v
USB / RS-485 ADAPTER
    |
    v
WINDOWS PC
    |
    v
Python / telescope software

The computer could continuously receive:

Elevation = 37.42 degrees

WHY RS-485 IS ATTRACTIVE

RS-485 is:

Cheap
Reliable
Suitable for long cables
Resistant to electrical interference
Easy to connect to a computer
Easy to read using Python

This is preferable to Bluetooth for a permanent observatory installation.

ANALOGUE ALTERNATIVE

Another simple arrangement would be:

Dish
  |
  v
0-5 V inclinometer
  |
  v
ADC
  |
  v
Arduino / Raspberry Pi / PC

For example:

 0 degrees  -> 0.5 V
45 degrees  -> 2.5 V
90 degrees  -> 4.5 V

The exact relationship depends upon the particular sensor.

ACCURACY REQUIRED

For a 1.5 metre dish operating around 1420 MHz, extremely high precision isn’t necessary.

Something with approximately:

Resolution:  0.1 degree
Accuracy:    +/-0.1 to +/-0.2 degree

would already be very useful for dish pointing.

Industrial sensors offering:

0.01 degree resolution

would be more than adequate.

IMPORTANT DISTINCTION

There are therefore two slightly different products:

1. HANDHELD DIGITAL ANGLE GAUGE Gravity | v Sensor | v LCD 37.4 degrees Cheap and convenient, but usually no computer output.
2. INDUSTRIAL DIGITAL INCLINOMETER Gravity | v Sensor | v Digital output | v RS-485 | v Computer | v 37.42 degrees Better for an automated radio telescope.

MY PREFERRED ARRANGEMENT

For your radio telescope I would use:

DISH
  |
  +-- +/-90 degree gravity inclinometer
              |
              | RS-485
              |
         outdoor cable
              |
              v
      USB-RS485 converter
              |
              v
         WINDOWS PC

This would provide a completely independent measurement of the REAL physical elevation of the dish rather than relying on motor position or calculated position.

It could also be used to calibrate the elevation drive:

COMMAND       INCLINOMETER

  0.0 deg  ->    0.2 deg
 20.0 deg  ->   20.1 deg
 40.0 deg  ->   39.8 deg
 60.0 deg  ->   59.9 deg
 80.0 deg  ->   79.7 deg
 90.0 deg  ->   89.8 deg

That would allow you to generate a correction table for the dish pointing system.