Watlow SDMA Card Shorted Solid State Relay Detector User Manual

There is concern that if a solid state relay fails, it will
most likely fail in a shorted condition. To minimize this
concern, Watlow Controls has designed a low-cost card
(Watlow P/N 09-2313) that provides a shorted SSR
alarm. It is designed to be used with DC input SSRs,
rated 10 to 40 amps on either a single phase or three­phase, two-leg system. In addition to the SDMA card, we
strongly recommend semiconductor fuses to protect the
SSR, and a high limit cutout to protect the thermal
system from any runaway conditions.

The SDMA card mounts directly on the solid state relay
and takes its power from the current flowing through the
current transformer. If there is no input command signal
from the temperature control to the SSR, and there is
current flow through the heater, the mechanical relay
alarm output will de-energize. This can be wired through
a customer supplied latching relay and alarm to 120 or
240 volts. Output contact rating of the SDMA mechanical
relay is 0.5 amperes maximum.

Watlow Controls

1241 Bundy Blvd., P.O. Box 5580

Winona, MN 55987-5580

Phone: [phone], Fax: [phone]

SDMA Card

Shorted Solid State Relay Detector

Data Sheet

0600-0028-0006 Rev A (1632) Made in the U.S.A.

January, 1999

Figure 1 - SDMA Card Dimensions

NOTE: Mount with two 6-32 screws 5/8”
long. (Included with the SDMA card.)

Load Number of Passes of Load Wire

Current Through Current Transformer

2 to 3 Amps 5
3 to 4 Amps 4
4 to 5 Amps 3

5 to 10 Amps 2

10 to 40 Amps 1

Figure 3 - SDMA Card Wiring

Table 1 - Application of 16-0231 Current Transformer

Figure 2 - Three Dimensional View of Wiring

NOTES:
Include a flyback diode across the external
latching relay coil. See D1.

To form a logic chain alarm, place multiple
SDMA alarm outputs in series.

Alarm

1 2

Alarm

1 2

V~ (ac)

Heater

S D M A

CT

Alarm

1 2 1 2Normally Closed

Contact

- 24V +

D1

RYI Contacts

External Latching Relay

24V (dc) Coil

RY1

Coil

SW1

Momentary

Reset Switch

+

-

24V (dc)

(Customer Supplied)

Minimum of 21mA

supply current

(per SDMA card)

is required.