Is it possible to read Wh to 2 digits of precision on the PM5000 range?

JamesAZZO · ‎2014-02-25

We can see on the front panel that kW power readings have 5 decimal places. Is it possible to read the 5 decimal places in Modbus comms? Consequently, will you also be able to read kWh to that same 5 digits of precision?

Robert_Lee · ‎2014-03-03

Hi James,

I'll try and answer your question as I've done some work with all the PM5XXX devices. The Power parameters are passed via Modbus using standard IEEE 754 Float32 notation using 2 16-bit registers. This will allow Power parameters such as kW to have up to 7 significant digits. Thus for low power readings the front panel can display up to 5 decimal places (but as readings increase the # of digits after the decimal will reduce). Software like ION:S may display using some type of fixed decimal representation or could dynamically adjust but showing more significant digits is meaningless.

For energy registers, the PM5XXX series passes values as an INT64 register in 4 x 16 bit registers (which represents only whole numbers without any decimals) but are passed at the lowest possible unit (ex. Wh instead of kWh). Thus depending on how the software wants to display this information this could show up to 3 decimals (i.e. if they show the label as kWH, then the number would be divided by 1000).

The front panel looks like it will still show this value with decimal places but those decimal places will never have any significance (i.e. lowest unit is 1 Wh which will show on the display as 1.0000 Wh). Only whole numbers of Wh will be contained in the registers.

Hope this answers your questions.

See Answer In Context

JamesAZZO · ‎2014-03-02

Anyone?

sesa186702 · ‎2014-03-02

What are you mentioning here? Power (kW) or Energy consumption (Wh) ?

JamesAZZO · ‎2014-03-02

Both actually, per my questions above.

We can see that kW (power) shows 5 decimal places on the front panel at low loads but Modbus only shows 3. Similar for kWh, but that might be because of the amount of whole digits able to be shown on the front panel. Software shows 3 decimals, similar to kW.

Robert_Lee · ‎2014-03-03

Hi James,

I'll try and answer your question as I've done some work with all the PM5XXX devices. The Power parameters are passed via Modbus using standard IEEE 754 Float32 notation using 2 16-bit registers. This will allow Power parameters such as kW to have up to 7 significant digits. Thus for low power readings the front panel can display up to 5 decimal places (but as readings increase the # of digits after the decimal will reduce). Software like ION:S may display using some type of fixed decimal representation or could dynamically adjust but showing more significant digits is meaningless.

For energy registers, the PM5XXX series passes values as an INT64 register in 4 x 16 bit registers (which represents only whole numbers without any decimals) but are passed at the lowest possible unit (ex. Wh instead of kWh). Thus depending on how the software wants to display this information this could show up to 3 decimals (i.e. if they show the label as kWH, then the number would be divided by 1000).

The front panel looks like it will still show this value with decimal places but those decimal places will never have any significance (i.e. lowest unit is 1 Wh which will show on the display as 1.0000 Wh). Only whole numbers of Wh will be contained in the registers.

Hope this answers your questions.

JamesAZZO · ‎2014-03-03

Thanks Robert! Exactly the answer I needed (although not what I was hoping for). I figured it was only measuring in Wh. If you can believe this, we have a customer who wants to be measuring energy down to the 0.00 of a Wh. (not kWh) - crazy and unmeaningful in 99.99999 of cases.