PF2100 4-20mA Input Card User Manual v1.2
©2021 Profire Energy Inc
June 2, 2021
Page 9
1.
Run the PF2100 on 15V
–
When the PF2100 is configured through its menu for 12V operation, it can safely run on anything from 10V-15.5V without
causing a low or high voltage alarm. It is therefore safe to set the system to run from 15V and connect the transmitter
up to the “12/24V”
pin on the 4-
20mA Card which will output 15V.
2.
Run the PF2100 on 24V
–
Many transmitters can run on a system voltage of 24V or higher. The Rosemount 2088 can run on as much as 36V. If you
change the PF2100’s menu settings to expect 24V
using menu 4.8 and then change its power supply to 24V, the “12/24V” pin on the 4
-20mA Card will
also output 24V which can be used to power the transmitter.
3.
Use a Separate Power Supply
–
The PF2100 and the transmitter can run from separate power supplies if desired. The PF2100 can run from 12V or 24V
and the transmitter can run from some other voltage source as required. If you do this, ensure that the external supply has a common ground
connection with the PF2100 using a chassis ground or the ground pin provided on the 4-20mA Input Card.
Compensating for Cable Length
If your cable length is very long (>500 feet) and/or your wire gauge is very narrow (>16 AWG), you may also need to account for the DC resistance of the cable
(R
CABLE
). In most cases, the cable resistance is negligible and can be ignored (R
CABLE
= 0).
To account for cable resistance, first add up the total length of cable (L
CABLE
in feet) that runs from the voltage supply to the transmitter, from the transmitter to
the 4-
20mA Input Card’s “Level” input, and
the length of ground wire running from the Input Card back to the voltage supply.
Equation 3:
𝐿
𝐶𝐴𝐵𝐿𝐸
= 𝐿
𝑆𝑈𝑃𝑃𝐿𝑌−𝑇𝑂−𝑇𝑅𝐴𝑁𝑆𝐷𝑈𝐶𝐸𝑅
+ 𝐿
𝑇𝑅𝐴𝑁𝑆𝐷𝑈𝐶𝐸𝑅−𝑇𝑂−𝐶𝐴𝑅𝐷
+ 𝐿
𝐶𝐴𝑅𝐷−𝑇𝑂−𝑆𝑈𝑃𝑃𝐿𝑌
You will then need to look up the DC resistance from the cable’s datasheet which is typically specified in Ohms per thousand
feet at a given gauge and for a given
type (stranded vs non-stranded). Plug this into the following equation to determine the DC resistance of your cable:
Equation 4:
𝑅
𝐶𝐴𝐵𝐿𝐸
=
𝐿
𝐶𝐴𝐵𝐿𝐸
∗𝑅
𝑃𝐸𝑅_𝑇𝐻𝑂𝑈𝑆𝐴𝑁𝐷_𝐹𝐸𝐸𝑇
1000
Then use the corresponding equations to determine the minimum supply voltage. If powering the transmitter via. the 4-20mA card use Equation 5, if powering
the transmitter from a separate power supply use Equation 6:
Equation 5:
𝑉
𝑃𝐹2100_𝑀𝐼𝑁
= 𝑉
𝑇𝑅𝐴𝑁𝑆𝐷𝑈𝐶𝐸𝑅_𝑀𝐼𝑁
+ 4.44𝑉 + 𝑅
𝐶𝐴𝐵𝐿𝐸
∗ 0.02
Equation 6:
𝑉
𝑆𝑈𝑃𝑃𝐿𝑌_𝑀𝐼𝑁
= 𝑉
𝑇𝑅𝐴𝑁𝑆𝐷𝑈𝐶𝐸𝑅_𝑀𝐼𝑁
+ 3.24𝑉 + 𝑅
𝐶𝐴𝐵𝐿𝐸
∗ 0.02
Example Compensating for Cable Length
As an example, let’s again consider
the Rosemount 2088 but this time with a non-negligible 1000 feet of 20 gauge stranded wire. If the wire had a datasheet
resistance of 11 Ohms per thousand feet, using Equation 5, the new minimum voltage supply would be 15.16V (0.2V higher than before).
