Dwyer PMT - Manual (Page 19)

Particulate Monitoring Systems
Installation & Operating Manual
Document No. 210-1015-F Page 13 ©2007
7. Startup
7.1 4-20mA Loop Check
Upon initial installation the 4-20mA loop connection should be tested. Monitor the transmitter’s mA
output with a multimeter connected in series with the 4-20mA loop or monitor the PLC register or
measuring device.
Step 1: Check the transmitter’s 4mA output by setting the output range switch to the “4mA Test”
position. The output should be 3.9mA – 4.1mA. If the output is not within the range specified, check
the following:
Output = 0mA – check for proper termination of all wires, check for proper connection of
multimeter, ensure loop power supply is on.
Output not between 3.9mA - 4.1mA - ensure loop voltage measured across the transmitter input
terminals is 18 – 28VDC.
Step 2: Verify the reading at the recording device (PLC, etc.) is reading the equivalent of 4mA.
Step 3: Check the transmitter’s 20mA output by setting the output range switch to the “20mA Test”
position. The output should be 19.9mA – 20.1mA. If the output is not within the range specified,
check the following:
Output not between 19.9mA – 20.1mA – ensure loop voltage measured across the transmitter
input terminals is 18 - 28VDC. If the loop voltage is within the allowable range, ensure that the
external loop impedance does not exceed that allowed for loop compliance. Calculate maximum
allowable external loop impedance (Rmax) as follows:
) ( 0 . 20
) ( 0 . 14 ) (
) max(
mA
vdc vdc Vloop
R
−
= Ω
Step 4: Verify the reading at the recording device (PLC, etc.) is reading the equivalent of 20mA.
Note: If a multimeter is connected in the series current loop,
its impedance will be added to that of the plc/dcs analog input
impedance.