TURTLE
TOUGH
®
30
Frequently Asked Questions for TT-MA
pH, ORP, ISE, Dissolved Oxygen & Conductivity
transmitters & controllers with application notes
Can I share the 24VDC power supply used to energize other instrumentation or equipment at the same installation site to also
energize the TT-MA transmitters?
Absolutely not.
It is altogether critical that the 24VDC power supply used to power the TT-MA transmitters is COMPLETELY separate from all
other equipment.
This also includes all other instrumentation as well other heavier equipment such as pumps, motors and so forth.
This is because the TT-MA measurement module series is a 3-wire transmitter. The 3-wire aspect can be explained as follows: the
4-20mA analogue current loop output sent from terminal 7 returns back to terminal 8; the +24VDC is connected to terminal 6 while
the ground DC common from the power supply is shared with the return of the 4-20mA scalable current loop output on terminal 8. In
this way all of the ground terminal are shared between the current loop output and the DC common amongst all TT-MA measurement
modules energized from a single 24VDC power supply source. There exists a 3000V opto-coupler isolation between the inputs and
outputs of the TT-MA transmitter no matter the particular measurement module. The outputs are not, however, isolated from each
other as the ground terminal is shared in the manner described above. Because of these reasons whatever 24VDC power supply is
used to energize the TT-MA transmitters should be altogether dedicated to only power these modules only. This dedicated 24VDC
power supply can either be customer supplied or using the Turtle Tough supplied TT-MA-PS module.
The 35mm DIN-RAIL mountable TT-MA-PS power supply offer a very simple and low-cost solution for the TT-MA transmitters to
have their own dedicated 24VDC power supply as required. It is also quite compact being only half the width of a standard TT-
MA module and 35mm DIN-RAIL mountable and so readily fitting into any of the enclosure options. When purchased as part of a
complete DIN-RAIL mounted or enclosure assembled configuration, the TT-MA-PS module will be pre-wired to all of the TT-MA
transmitter(s) supplied so that only the AC power input for the TT-MA-PS need to be added to have the unit(s) up and working (plus
connecting the analogue and MODbus outputs as well as the sensors for input as usual).
The TT-MA-PS is a well-tested proven power supply solution at very many customer installation sites. The issue of having a dedicated
24VDC power supply for the TT-MA modules is important for both passive input measurement module types such the TT-MA-pH,
TT-MA-ISE (mate with pH/ORP/ISE sensors without preamplifiers) and TT-MA-DO (mate with galvanic DO cells) as well as active
input measurement module types such as the TT-MA-pH-X, TT-MA-ISE-X (mate with pH/ORP/ISE sensors with preamplifiers) and
TT-MA-CON (all contacting conductivity cells). The isolation on the AC/DC transformer of the TT-MA-PS acts to isolate the 24VDC
power from the rest of the electrical devices at the installation site ensuring that no such potential ground issues occur to the modules
themselves nor any devices powered from the TT-MA measurement modules such as preamplifiers and contacting conductivity cells.
This isolation in the TT-MA-PS also serves to ensure that no issues prevent themselves regarding ground on the analogue 4-20mA
current loop output or RS485 MODbus outputs emanating from the power supply side of the system. It is still possible to have ground
loop and electrical isolation issues that emanate from the process side of the system, but this is a much more complex question and
larger in scope than just the TT-MA instrumentation.
The TT-MA-PS power supply has a 500mA max rating at 24VDC (12 Watts) and easily handles up to 8 each TT-MA modules with
60mA as the absolute max power consumption per TT-MA module unit. The TT-MA-PS is a universal 100 to 240 VAC 50/60 Hz
power supply module. The agency approvals for the TT-MA-PS module includes CE, CSA & UL for use in safe areas. If you plan to
install the TT-MA transmitters into a hazardous area please inquire Turtle Tough for special accommodations necessary to support
these application and installation types.
Please see the next page for Power wiring connection diagrams.
How do you wire up the analogue output from the TT-MA transmitter to a data acquisition or control system?
Keep in mind that all TT-MA transmitters are 3-wire devices. This means they have an ACTIVE 4-20mA analogue current loop out
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put, like a 4-wire type device. The data acquisition or control device to which this TT-MA active 4-20mA output is connected should
passively measure the current. Most PLC have a hardware or software toggle that allows you to select whether the 4-20mA received
is from a 4-wire (or 3-wire) active type device or else if it is a 2-wire device which must be energized from the PLC power supply.
NEVER apply voltage across terminals 7 & 8 on any TT-MA transmitter! This could happen if a 3-wire type TT-MA transmitters is wired
as though it were a 2-wire type devices. The result of such an improper wiring would destroy the output circuit with the damage
not covered under warranty due to abuse/misuse.
The lead pro24VDC power always goes to terminal 6 and the 4-20mA current loop output is always sent from terminal 7.
The DC common (ground) is shared as terminal 8. The current loop output is sent from terminal 7 and return to terminal 8 (ground
/ DC common). The TT-MA transmitters are always energized on terminal 6 with the DC ground of the 24VDC power supply (a.k.a.
rail) always being the (shared) terminal 8.
