Streckeisen STS-2; 120 s ... 30 Hz(*)

(*)There are also some instruments with upper corner frequency of 50 Hz.

The poles and zeros below are the main ones.
Depending on serial number additional poles and zeros exist.

Gs = 1500 V/(m/s)

2 Zeros
z1 = 0
z2 = 0

2 Poles
p1 = -0.037   0.037i
p2 = -0.037  -0.037i

Normalisation Factor (@1Hz)
a = 1