Hi,

i have been struggling to get my drive to change speed via the rs485

uss protocol stack.

Has anyone used a digital variable resistor to do speed control

via the analogue pot terminals?

I have started looking at various chips to try and construct a circuit - 

but there might already be ready made hardware that has been tried/tested

as usual any help most appreciated. 

Hello.

it would be nice if you could explain your idea more clearly. How is the digital pot a replacement for the serial coms? What is the issue with the serial coms and why are you not using analog directly?

Have a look if your drive has a "speed up" and "speed down" functionality. People have used this concept as a digital adjustment on other drives. Perhaps this can work for you if available.

Good health and sanity.

Bonus tip..
A problem I have seen many times with RS485 communications is the lack of terminating resistors and both ends of the bus.

Hi thanks for response,

please see my other two posts where  i explain

what i am trying to do.

my drive is an older model - MM150.

This is not an issue with the communication physical link, i can read and write parameters

and switch the motor on and off via rs485.  

i cannot get the speed to change whilst the motor is running - i want to 

adjust the speed via a constant surface speed function from a cnc program.

constant surface speed is a function of a lathes infeed/outfeed on the lathes

X axis as a physical part is turned down. the smaller the reduction in diameter the faster

the motor speeds up.  conversely down.

as i cannot get the data to make my drive function and i have spent months trying to

get it to work. i decided to use a bcd signal to vary the analogue terminals via

a digital variable resistor module.  

hope that helps clarify your question

Hello.

You reply helps to explain your thoughts.

I do not know the specific drive you are working with. It is strange for me to hear that the drive speed cannot set with USS. The drive should be able to listen to USS for a setpoint just as it would an analog. It is a special register, it is not a parameter adjustment register.

Is a frequency to voltage converter an option to you? That would mean your controller needs to supply a frequency pulse. Or if it is a PWM, the width adjusted pulse can be filtered to an analog signal.

...I would have changed the drive by now.

If no user gives helpful answers to you, consider registering a formal request with Siemens. Use the "Support Request" button on this page. I am hopeful that there is a solution in USS.

Good luck.

Hi,

Thanks.

i cant change the drive. 

i know what you mean about it been speed adjustable - i just don't know which

parameters on the mm150 to use i have tried so many of them in various combinations

too numerous to mention.

basically the drive is not using the PZD HSW word frequency setpoint values

to change the speed - i can only get it to use the digital frequency set point 

in P005 - if i try any thing else the motor wont start or just locks up.

Please note i have all the correct settings regarding the other 

USS protocols for starting and stopping - STW Set is 8C 7E

Run is STW 14 7F ( motor turns Left) etc

i can read and set almost every parameter via the link. just not the speed

i can set the frequency setpoint - but the running motor never speeds up.

once i stop it and start it picks up the new frequency setpoint so its going in and storing it and

reading it.

I am looking at maybe analogue voltage injection or variable pwm 

i'm just looking at what solutions others have tried. NOT PLC control

that's more than i can afford.

Hi again,

you just triggered a memory. 

there are some settings called fixed frequency P041 to P044 on my drive

you have to set P006 Frequency setpoint source select to setting 2

which is :- 

2 =Fixed frequency or motor potentiometer. Fixed frequency is only selected if the value of at least one binary input (P051-P053) = 6, 17 or 18.

and  P051 to P053 are: -

P051 DIN1, FF3 function select

mine default to P051 = 1, P052 = 1 and P053 = 6 (Fixed frequencies 1 - 3)

im wondering if its these that are incorrect i tried changing these a while back but

never got any of them to function

sorry i copy and pasted and the table is out of alignment

Hi

this is now resolved thanks to help from

Tractor,  see  posting  

micro master speed change

Hellerzal-12345

Hi

this is now resolved thanks to help from

Tractor,  see  posting  

micro master speed change

That is brilliant news!  Thank you for making the update.

I did see the exchange you mention. Luckily you gave this problem the effort. It sure does help if you can talk to someone with experience.

You are welcome to mark your topics as solved. (there is an 'action' available on the topic)

Best health and sanity.

Hi,

thanks for all your help too

i have marked the action now