Introduction

The 843ES safety encoders from Allen-Bradley are designed to replace the Kuebler safety encoders on the telescope mount. The main reason is that we will then be able to read in the telescope’s actual position into the safety controller to provide additional safety functions (such as on-sun ephemeris calculations). In addition the old Kuebler system is no longer in production.

The intent was to provide a ‘drop-in’ replacement for the safety encoder. Due to on-going operational demands and safety concerns it was decided to mount the Allen-Bradley safety encoder on the same shaft as the Kuebler encoder and run both systems in parallel (at least for initial testing of the azimuth axis).

Documentation

EtherNet/IP Absolute Encoders: Standard and CIP Safety Models -- Installation Instructions

EtherNet/IP Absolute Encoders: Standard and CIP Safety Models -- User Manual

EtherNet/IP Network Devices

Setup

Setup is very briefly covered in the Installation Instructions. The important information you need to know is buried in the user manual. The 843ES is protected by a relatively new security 'enhancement'. It features mode for Implicit Protection mode and Explicit Protection mode. Implicit Protection mode is automatically turned on when the device is the target of (or bridges) any I/O connections.

When it is in Implicit Protected mode, the device helps prevent execution of the following tasks:

• Changing Ethernet configuration settings, such as port speed.

• Changing IP settings, such as IP address, mask, and DHCP mode.

• Updating the device firmware.

• Disabling or re-enabling external product ports.

• Performing remote resets.

As you can see setup is essentially impossible in Implicit Protected mode.

Explicit Protected mode is manually enabled by setting the internal switches to ‘900’ and powering up the device. Explicit Protected mode is manually disabled by setting the internal switches to ‘000’ and powering up the device. See the user manual for more information. Explicit Protected mode should not be used.

How to really set up an 843ES encoder

1. Connect Ethernet/IP cable directly to programming computer/laptop.

2. Set internal switches to ‘888’.

3. Power up 843ES. This will restore factory default settings.

4. Power down 843ES.

5. Set internal switches to ‘999’.

6. Power up 843ES.

7. Using BOOTP assign address (such as 10.4.1.21) to 843ES.

8. Using RSLinx Classic, under device properties, change ‘Obtain IP address automatically using DHCP’ to ‘Configure IP address manually.’

9. Power down 843ES.

10. Turn off BOOTP / DHCP servers on programming computer/laptop.

11. Power up 843ES.

12. Ping the assigned IP address to ensure the 843ES has retained the IP address and is correctly programmed.

13. If this fails, ensure that there are no I/O connection to or through the 843ES. Repeat above steps.

How to 'home' the 843ES encoder

Before the 843ES can be used it will need to be ‘homed.’ This process is very straight forward but it is critical to ensure it is properly completed.

1. Determine the precise position of the telescope axis. This can most likely be determined from the actual position as reported by the Beckhoff controller.

2. Enter the actual position of the telescope axis in the appropriate tag in the telescope LIC.

   1. Telescope Altitude Alt_HomePosition

   2. Telescope Azimuth Az_HomePosition

3. Toggle the appropriate bit to set the home position.

   1. Telescope Altitude HMI_TEL_Alt_HomePosition which is mapped to safety tag Tel_Enc_Alt_HomeTrig

   2. Telescope Azimuth HMI_TEL_Az_HomePosition which is mapped to safety tag Tel_Enc_Az_HomeTrig

4. Verify that the encoder position changes to match the home position.

   1. Telescope Altitude Altitude_SFX.ActualPosition

   2. Telescope Azimuth Azimuth_SFX.ActualPosition