We need a DAQ that can measure a pressure sensor at high frequency (5Khz). Is there something available on the market that is modbus RTU or TCP?

We have selected a pressure sensor that gives raw output in Volts, so no additional conversions to 4-20mA.

We normally use Wago 750 series fieldbuses, which are modbus TCP, but they cannot poll faster than about 80ms per poll, due to all kinds of internal conversions on the fieldbus. Any advice?

 

> Is there something available on the market that is modbus RTU or TCP?

Not that I'm aware of, but I'm not a professional shopper in that 5Khz field.

I'm a (relatively) low speed process control HMI & SCADA guy, where 0.1 to 1 second polling rates are fairly standard. 5Khz is not a typical HMI Modbus polling rate.

I thought the custom Modbus programmers would have popped up by now, but in their absence, I'll give it shot.

Profibus PA runs over RS-485 at up to 12Mb rates at a maximum 100m cabling distance, 1.5Mb at 200m. No reason why Modbus could not run over RS-485 at the same speed, if the master and slave were designed to do so. A 5KHz Modbus RTU request and reply exchange for a single, 16 bit integer value would require ~ 1.25Mb rate.

An 8,N,1 data word is 10 bits. (yes, the standard says even parity and 11 bits, but 8,N,1 is ubiquitous)
3.5 character silent period between frames (=35 bits)
An RTU function code 03 read request is 10 bytes (100 bits)
3.5 character silent period between frames (=35 bits)
An RTU single register slave reply is 6 bytes (60 bits)
Total (request, silence, reply, silence) is 250 bits of time.
5Khz read rate would be 5,000/sec*250 bits = 1,250,000 bits/sec
If an 11 bit word is used, then the rate is low by 10%

I'm aware that the "Modbus over serial line V1.02" standard recommends a 1.750mS interframe (3.5 character) frame delay (page 14). That's considerably longer than the equivalent of 3.5 characters (35 bits) at 1.25Mb baud rate.

But I suspect that this might turn out to be a custom project to achieve that rate of transfer.

This doesn't sound like a commercial effort, rather it sounds like a onesie, so whatever is agreed upon by the master and the slave should work.