SITRAINS LR250 & RD100

Hi,

I've got an LR250 transmitter and RD100 display which are to be connected with 24DC power supply, based on loop back power (HART protocol compliant)

A slight confusion on the wiring diagram which are attached. The first one is from SIEMENS web based documentation and show the -ve of the transmiiter connected with the +ve of RD100. However, te second diagram which came along the instrument documentation show the -ve of transmitter connected to the -ve of RD100.

Logically, the conncetions should be like this. From +ve of Power supply to the +ve of transmitter, then from -ve of transmitter to the +ve of RD100, and finally from -ve of RD100 to the -ve of P.Supply. 

Please suggest so that the instruments work perfectly.

Your assessment is on target.

If the RD100 terminals are labeled properly in the doc included with the instrument (the diagram you included in your post), then your description is absolutely correct and is confirmed by the correct wiring shown in the middle wiring diagram in your attached diagram.   The transmitter/power supply should then operate like any other loop powered transmitter connected to an indicator 4-20mA input.

As to the web misinformation, it isn't first and it won't be the last.  I lost a full day one time trying to get a flow meter frequency output to read into a freq input indicator because the Siemens documentation was incorrect.

Go for it.

dear Danw,

The instruments work as described above. But i get anADC/DAC error message on analog input.

Attached is the diagnostic buffer pic.

Toverify that the AI card is fine, i changed the eixisting with the newer one but the error is there.

The error (SF red light) is gone by downloading the HW configuration via Sematic Manager instead of TIA. Still got no clue of what the problem was while using TIA portal (V15). Probably of the firmware version which the sematic manager used was a bit of older version.

Now the Analog Cards are having zeros in all channels and field instrument showing no readings. However, when i bypass the AI  and the -ve from field is connected to -ve of battery, the instuments work fine.

Attached is pic. 

That's called a sucker punch.  All you mentioned in the first post was LR250 and an RD100.  With a power supply to drive both units, that's a loop.

Now you add another never mentioned AI.

The additional AI can go on either side of the RD100.   The diagram at the link shows the additional AI between the transmitter and the RD100.   It could go between the RD100 and power supply (-).

The AI (+) connects to the most positive side of the circuit, closest to the power supply (+).

Dear Dnaw,

My appolgies for missing the AI at initial post, as assumed the AI woud work fine with both as i did for only transmitter in past ( RD100 not included)

As you mentioned in the post that AI can go on either side of RD100, so for now the AI is between RD100 and -ve of Power Supply (attached pic). But still no reading at AI.

the Diagnositc Status of the AI cards is also attached

Dear Dnaw,

Let me explain.

I've a 315-2 PN/DP CPU. 3 number of AI attached are 8x12BIT (331-7KF02-0AB0). A 24VDC is installed powering up the PLC, I/O cards and the instruments in field (9 number of RD100 and 9 number of LR250 each pair connected in loop with one channel of AI). please see attachment.

1. when AI is bypassed, the instruments (LR250 & RD100 in loop with 24VDC) work and show reading on the display. However, when AI is looped ( as shown in attached fig.) there is no display in the field instruments, and the AI channel shows a reading of -32768 ( in fact all channels showing -32768).

2. Since the instruments in loop (from +ve of 24VDC PS to +ve of LR250 & then form -ve of LR250 to +ve of RD100 & from -ve of RD100 and finally to -ve of 24VDC PS) are showing values, this means the power source is enough drive field devices. Display of instruments and disappear when AI channel is included in the loop, and AI channel showing -32768 when monitored online.

3. -ve of AI channel is connected to -ve of 24VDC.

4. 24VDC supply is used

5. no resistance is used

6. the instruments are only 4-20 mA compliant working on HART protocol. No switching or jumpers are required.