Tango Device Server States : the "OFF" case.

# 4 years ago
Olivier Neveu	Hello, I am a computer scientist at Paris-Saclay university. My job is to write little programs to communicate with scientific instruments on a Petawatt class Laser of the university : "Laserix". I was recently asked to work on the "ThomX" scientific installation. The control command of this installation was built with Tango. I have a question that is not very important but my colleagues and I are curious : what is the purpose of the "OFF" state ? How is it possible to know that the device is not powered ? For instance : how to distinguish this state from a broken connection ? I can see an example : by querying a controllable electrical outlet to which the device is connected ? Is there another example where the state of a device server can be unequivocally set to OFF ? Best reguards, Olivier Neveu

# 4 years ago

Hello,

I am a computer scientist at Paris-Saclay university.
My job is to write little programs to communicate with scientific instruments on a Petawatt class Laser of the university : "Laserix".
I was recently asked to work on the "ThomX" scientific installation.
The control command of this installation was built with Tango.
I have a question that is not very important but my colleagues and I are curious : what is the purpose of the "OFF" state ?
How is it possible to know that the device is not powered ? For instance : how to distinguish this state from a broken connection ?
I can see an example : by querying a controllable electrical outlet to which the device is connected ?
Is there another example where the state of a device server can be unequivocally set to OFF ?

Best reguards, Olivier Neveu

# 4 years ago
Reynald	Olivier Neveu what is the purpose of the "OFF" state ? How is it possible to know that the device is not powered ? For some hardware devices, it is possible to know that they are switched off. Their controller is not switched OFF so the Tango device server is still connected to the controller and the controller can give the state of the subsystems it is controlling. For instance a motor controller can give the state of a motor. It can switch it ON or OFF. The same for a power supply which can be controlled remotely. Another example can be a Tango device representing a network port using power over ethernet. The Tango device server can communicate with the network switch which can control the state of the different network switch ports. It is possible to switch OFF or ON the power on the network switch ports. Olivier Neveu For instance : how to distinguish this state from a broken connection ? We usually use the UNKNOWN state to represent a broken connection. Olivier Neveu I can see an example : by querying a controllable electrical outlet to which the device is connected ? Is there another example where the state of a device server can be unequivocally set to OFF ? A Tango device can also be a pure software device. So it can represent a correction loop for instance. The OFF state could be chosen to represent the state when the loop is not active for instance. Rosenberg's Law: Software is easy to make, except when you want it to do something new. Corollary: The only software that's worth making is software that does something new.

# 4 years ago

Reynald

Olivier Neveu
what is the purpose of the "OFF" state ?
How is it possible to know that the device is not powered ?

For some hardware devices, it is possible to know that they are switched off. Their controller is not switched OFF so the Tango device server is still connected to the controller and the controller can give the state of the subsystems it is controlling.
For instance a motor controller can give the state of a motor. It can switch it ON or OFF.
The same for a power supply which can be controlled remotely.
Another example can be a Tango device representing a network port using power over ethernet.
The Tango device server can communicate with the network switch which can control the state of the different network switch ports.
It is possible to switch OFF or ON the power on the network switch ports.

Olivier Neveu
For instance : how to distinguish this state from a broken connection ?

We usually use the UNKNOWN state to represent a broken connection.

Olivier Neveu
I can see an example : by querying a controllable electrical outlet to which the device is connected ?
Is there another example where the state of a device server can be unequivocally set to OFF ?

A Tango device can also be a pure software device. So it can represent a correction loop for instance. The OFF state could be chosen to represent the state when the loop is not active for instance.

Rosenberg's Law: Software is easy to make, except when you want it to do something new.
Corollary: The only software that's worth making is software that does something new.

# 4 years ago
pgoryl	Hi Olivier, The OFF state does not necessarily relate to the power state of a device one communicate with. It is a case when some other device is controlled through a digital output card or a PLC. For example, a bulb may be switched on and off by means of a PLC relay output. All the best, Piotr

# 4 years ago
Hiro	Hello Olivier, Every Tango state are not meant to be used in every devices and, as they are limited, there is sometimes no exact match with the exact needs of a device. So OFF state may not be used as real "switched off" state. I'm pretty sure that equipment may have feature to be switched on/off from a distance, perhaps using other devices (or using controlled outlet as you mentioned) or even some Wake-on-Lan features. Here at Thales, we have only one usecase of the OFF state on some of our laser pumps that have a "Stopping" state. Best regards Guillaume DI FRANCO Thales - Software Engineer Manager

# 4 years ago

Hiro

Hello Olivier,

Every Tango state are not meant to be used in every devices and, as they are limited, there is sometimes no exact match with the exact needs of a device. So OFF state may not be used as real "switched off" state.
I'm pretty sure that equipment may have feature to be switched on/off from a distance, perhaps using other devices (or using controlled outlet as you mentioned) or even some Wake-on-Lan features. Here at Thales, we have only one usecase of the OFF state on some of our laser pumps that have a "Stopping" state.

Best regards

Guillaume DI FRANCO
Thales - Software Engineer Manager

# 4 years ago
Olivier Neveu	Hello all of you, thank you very much for your helpful comments. Best regards, Olivier